ACE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track L. Seitz
Expires: 12 January 2023 Combitech
F. Palombini
Ericsson AB
S. Echeverria
G. Lewis
CMU SEI
11 July 2022
Notification of Revoked Access Tokens in the Authentication and
Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-revoked-token-notification-02
Abstract
This document specifies a method of the Authentication and
Authorization for Constrained Environments (ACE) framework, which
allows an Authorization Server to notify Clients and Resource Servers
(i.e., registered devices) about revoked Access Tokens. The method
allows Clients and Resource Servers to access a Token Revocation List
on the Authorization Server, with the possible additional use of
resource observation for the Constrained Application Protocol (CoAP).
Resulting (unsolicited) notifications of revoked Access Tokens
complement alternative approaches such as token introspection, while
not requiring additional endpoints on Clients and Resource Servers.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Authentication and
Authorization for Constrained Environments Working Group mailing list
(ace@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ace/.
Source for this draft and an issue tracker can be found at
https://github.com/ace-wg/ace-revoked-token-notification.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
3. Token Hash . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. The TRL Resource . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Update of the TRL Resource . . . . . . . . . . . . . . . 10
5. The TRL Endpoint . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Supporting Diff Queries . . . . . . . . . . . . . . . . . 12
5.1.1. Supporting the "Cursor" Extension . . . . . . . . . . 13
5.2. Query Parameters . . . . . . . . . . . . . . . . . . . . 14
6. Full Query of the TRL . . . . . . . . . . . . . . . . . . . . 16
7. Diff Query of the TRL . . . . . . . . . . . . . . . . . . . . 17
8. Using the "Cursor" Extension . . . . . . . . . . . . . . . . 20
8.1. Response to Full Query . . . . . . . . . . . . . . . . . 20
8.2. Response to Diff Query . . . . . . . . . . . . . . . . . 21
8.2.1. Empty Collection . . . . . . . . . . . . . . . . . . 21
8.2.2. Cursor Not Specified in the Diff Query Request . . . 21
8.2.3. Cursor Specified in the Diff Query Request . . . . . 23
9. Upon Registration . . . . . . . . . . . . . . . . . . . . . . 25
10. Notification of Revoked Tokens . . . . . . . . . . . . . . . 26
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11. Interaction Examples . . . . . . . . . . . . . . . . . . . . 27
11.1. Full Query with Observation . . . . . . . . . . . . . . 28
11.2. Diff Query with Observation . . . . . . . . . . . . . . 30
11.3. Full Query with Observation and Additional Diff Query . 32
12. ACE Token Revocation List Parameters . . . . . . . . . . . . 34
13. ACE Token Revocation List Error Identifiers . . . . . . . . . 35
14. Security Considerations . . . . . . . . . . . . . . . . . . . 36
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
15.1. Media Type Registrations . . . . . . . . . . . . . . . . 37
15.2. CoAP Content-Formats Registry . . . . . . . . . . . . . 38
15.3. ACE Token Revocation List Parameters Registry . . . . . 38
15.4. ACE Token Revocation List Errors . . . . . . . . . . . . 39
15.5. Expert Review Instructions . . . . . . . . . . . . . . . 39
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 40
16.1. Normative References . . . . . . . . . . . . . . . . . . 40
16.2. Informative References . . . . . . . . . . . . . . . . . 42
Appendix A. On using the Series Transfer Pattern . . . . . . . . 42
Appendix B. Document Updates . . . . . . . . . . . . . . . . . . 43
B.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 43
B.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 43
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 44
1. Introduction
Authentication and Authorization for Constrained Environments (ACE)
[I-D.ietf-ace-oauth-authz] is a framework that enforces access
control on IoT devices acting as Resource Servers. In order to use
ACE, both Clients and Resource Servers have to register with an
Authorization Server and become a registered device. Once
registered, a Client can send a request to the Authorization Server,
to obtain an Access Token for a Resource Server. For a Client to
access the Resource Server, the Client must present the issued Access
Token at the Resource Server, which then validates it before storing
it (see Section 5.10.1.1 of [I-D.ietf-ace-oauth-authz]).
Even though Access Tokens have expiration times, there are
circumstances by which an Access Token may need to be revoked before
its expiration time, such as: (1) a registered device has been
compromised, or is suspected of being compromised; (2) a registered
device is decommissioned; (3) there has been a change in the ACE
profile for a registered device; (4) there has been a change in
access policies for a registered device; and (5) there has been a
change in the outcome of policy evaluation for a registered device
(e.g., if policy assessment depends on dynamic conditions in the
execution environment, the user context, or the resource
utilization).
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As discussed in Section 6.1 of [I-D.ietf-ace-oauth-authz], only
client-initiated revocation is currently specified [RFC7009] for
OAuth 2.0 [RFC6749], based on the assumption that Access Tokens in
OAuth are issued with a relatively short lifetime. However, this is
not expected to be the case for constrained, intermittently connected
devices, that need Access Tokens with relatively long lifetimes.
This document specifies a method for allowing registered devices to
access and possibly subscribe to a Token Revocation List (TRL)
resource on the Authorization Server, in order to obtain an updated
list of revoked, but yet not expired, pertaining Access Tokens. In
particular, registered devices can subscribe to the TRL at the
Authorization Server by using resource observation [RFC7641] for the
Constrained Application Protocol (CoAP) [RFC7252].
Unlike in the case of token introspection (see Section 5.9 of
[I-D.ietf-ace-oauth-authz]), a registered device does not provide an
owned Access Token to the Authorization Server for inquiring about
its current state. Instead, registered devices simply obtain an
updated list of revoked, but yet not expired, pertaining Access
Tokens, as efficiently identified by corresponding hash values.
The benefits of this method are that it complements token
introspection, and it does not require any additional endpoints on
the registered devices. The only additional requirements for
registered devices are a request/response interaction with the
Authorization Server to access and possibly subscribe to the TRL (see
Section 2), and the lightweight computation of hash values to use as
Token identifiers (see Section 3).
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts
described in the ACE framework for Authentication and Authorization
[I-D.ietf-ace-oauth-authz], as well as with terms and concepts
related to CBOR Web Tokens (CWTs) [RFC8392], and JSON Web Tokens
(JWTs) [RFC7519]. The terminology for entities in the considered
architecture is defined in OAuth 2.0 [RFC6749]. In particular, this
includes Client, Resource Server, and Authorization Server.
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Readers are also expected to be familiar with the terms and concepts
related to CBOR [RFC8949], JSON [RFC8259], the CoAP protocol
[RFC7252], CoAP Observe [RFC7641], and the use of hash functions to
name objects as defined in [RFC6920].
Note that, unless otherwise indicated, the term "endpoint" is used
here following its OAuth definition, aimed at denoting resources such
as /token and /introspect at the Authorization Server, and /authz-
info at the Resource Server. This document does not use the CoAP
definition of "endpoint", which is "An entity participating in the
CoAP protocol."
This specification also refers to the following terminology.
* Token hash: identifier of an Access Token, in binary format
encoding. The token hash has no relation to other possibly used
token identifiers, such as the "cti" (CWT ID) claim of CBOR Web
Tokens (CWTs) [RFC8392].
* Token Revocation List (TRL): a collection of token hashes such
that the corresponding Access Tokens have been revoked but are not
expired yet.
* TRL resource: a resource on the Authorization Server, with a TRL
as its representation.
* TRL endpoint: an endpoint at the Authorization Server associated
with the TRL resource. The default name of the TRL endpoint in a
url-path is '/revoke/trl'. Implementations are not required to
use this name, and can define their own instead.
* Registered device: a device registered at the Authorization
Server, i.e., as a Client, or a Resource Server, or both. A
registered device acts as a caller of the TRL endpoint.
* Administrator: entity authorized to get full access to the TRL at
the Authorization Server, and acting as a caller of the TRL
endpoint. An administrator is not necessarily a registered device
as defined above, i.e., a Client requesting Access Tokens or a
Resource Server consuming Access Tokens. How the administrator
authorization is established and verified is out of the scope of
this specification.
* Pertaining Access Token:
- With reference to an administrator, an Access Token issued by
the Authorization Server.
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- With reference to a registered device, an Access Token intended
to be owned by that device. An Access Token pertains to a
Client if the Authorization Server has issued the Access Token
and provided it to that Client. An Access Token pertains to a
Resource Server if the Authorization Server has issued the
Access Token to be consumed by that Resource Server.
Examples throughout this document are expressed in CBOR diagnostic
notation without the tag and value abbreviations.
2. Protocol Overview
This protocol defines how a CoAP-based Authorization Server informs
Clients and Resource Servers, i.e., registered devices, about
pertaining revoked Access Tokens. How the relationship between a
registered device and the Authorization Server is established is out
of the scope of this specification.
At a high level, the steps of this protocol are as follows.
* Upon startup, the Authorization Server creates a single TRL
resource. At any point in time, the TRL resource represents the
list of all revoked Access Tokens issued by the Authorization
Server that are not expired yet.
* When a device registers at the Authorization Server, it also
receives the url-path to the TRL resource.
After the registration procedure is finished, the registered
device can send an Observation Request to the TRL resource as
described in [RFC7641], i.e., a GET request including the CoAP
Observe Option set to 0 (register). By doing so, the registered
device effectively subscribes to the TRL resource, as interested
to receive notifications about its update. Upon receiving the
request, the Authorization Server adds the registered device to
the list of observers of the TRL resource.
At any time, the registered device can send a GET request to the
TRL endpoint. When doing so, it can request for: the current list
of pertaining revoked Access Tokens (see Section 6); or the most
recent TRL updates occurred over the list of pertaining revoked
Access Tokens (see Section 7). In either case, the registered
device may also rely on an Observation Request for subscribing to
the TRL resource as discussed above.
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* When an Access Token is revoked, the Authorization Server adds the
corresponding token hash to the TRL. Also, when a revoked Access
Token eventually expires, the Authorization Server removes the
corresponding token hash from the TRL.
In either case, after updating the TRL, the Authorization Server
sends Observe Notifications as per [RFC7641]. That is, an Observe
Notification is sent to each registered device subscribed to the
TRL resource and to which the Access Token pertains.
Depending on the specific subscription established through the
observation request, the notification provides the current updated
list of revoked Access Tokens in the portion of the TRL pertaining
to that device (see Section 6), or rather the most recent TRL
updates occurred over that list of pertaining revoked Access
Tokens (see Section 7).
Further Observe Notifications may be sent, consistently with
ongoing additional observations of the TRL resource.
* An administrator can access and subscribe to the TRL like a
registered device, while getting the full updated representation
of the TRL.
Figure 1 shows a high-level overview of the service provided by this
protocol. In particular, it shows the Observe Notifications sent by
the Authorization Server to one administrator and four registered
devices, upon revocation of the issued Access Tokens t1, t2 and t3,
with token hash th1, th2 and th3, respectively. Each dotted line
associated with a pair of registered devices indicates the Access
Token that they both own.
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+----------------------+
| Authorization Server |
+-----------o----------+
revoke/trl | TRL: {th1,th2,th3}
|
+-----------------+------------+------------+------------+
| | | | |
| th1,th2,th3 | th1,th2 | th1 | th3 | th2,th3
v v v v v
+---------------+ +----------+ +----------+ +----------+ +----------+
| Administrator | | Client 1 | | Resource | | Client 2 | | Resource |
| | | | | Server 1 | | | | Server 2 |
+---------------+ +----------+ +----------+ +----------+ +----------+
: : : : : :
: : t1 : : t3 : :
: :........: :............: :
: t2 :
:...........................................:
Figure 1: Protocol Overview
Section 11 provides examples of the protocol flow and message
exchange between the Authorization Server and a registered device.
3. Token Hash
The token hash of an Access Token is computed as follows.
1. The Authorization Server defines ENCODED_TOKEN, as the content of
the 'access_token' parameter in the Authorization Server response
(see Section 5.8.2 of [I-D.ietf-ace-oauth-authz]), where the
Access Token was included and provided to the requesting Client.
Note that the content of the 'access_token' parameter is either:
* A CBOR byte string, if the Access Token was transported using
CBOR. With reference to the example in Figure 2, and assuming
the string's length in bytes to be 119 (i.e., 0x77 in
hexadecimal), then ENCODED_TOKEN takes the bytes {0x58 0x77
0xd0 0x83 0x44 0xa1 ...}, i.e., the raw content of the
parameter 'access_token'.
* A text string, if the Access Token was transported using JSON.
With reference to the example in Figure 3, ENCODED_TOKEN takes
"2YotnFZFEjr1zCsicMWpAA", i.e., the raw content of the
parameter 'access_token'.
2. The Authorization Server defines HASH_INPUT as follows.
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* If CBOR was used to transport the Access Token (as a CWT or
JWT), HASH_INPUT takes the same value of ENCODED_TOKEN.
* If JSON was used to transport the Access Token (as a CWT or
JWT), HASH_INPUT takes the serialization of ENCODED_TOKEN.
In either case, HASH_INPUT results in the binary
representation of the content of the 'access_token' parameter
from the Authorization Server response.
3. The Authorization Server generates a hash value of HASH_INPUT as
per Section 6 of [RFC6920]. The resulting output in binary
format is used as the token hash. Note that the used binary
format embeds the identifier of the used hash function, in the
first byte of the computed token hash.
The specifically used hash function MUST be collision-resistant
on byte-strings, and MUST be selected from the "Named Information
Hash Algorithm" Registry [Named.Information.Hash.Algorithm].
The Authorization Server specifies the used hash function to
registered devices during their registration procedure (see
Section 9).
2.01 Created
Content-Format: application/ace+cbor
Max-Age: 85800
Payload:
{
"access_token" : h'd08344a1 ...
(remainder of the Access Token omitted for brevity) ...',
"token_type" : pop,
"expires_in" : 86400,
"profile" : coap_dtls,
(remainder of the response omitted for brevity)
}
Figure 2: Example of Authorization Server response using CBOR
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HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-store
Pragma: no-cache
Payload:
{
"access_token" : "2YotnFZFEjr1zCsicMWpAA ...
(remainder of the Access Token omitted for brevity) ...",
"token_type" : "pop",
"expires_in" : 86400,
"profile" : "coap_dtls",
(remainder of the response omitted for brevity)
}
Figure 3: Example of Authorization Server response using JSON
4. The TRL Resource
Upon startup, the Authorization Server creates a single TRL resource,
encoded as a CBOR array.
Each element of the array is a CBOR byte string, with value the token
hash of an Access Token. The order of the token hashes in the CBOR
array is irrelevant, and the CBOR array MUST be treated as a set in
which the order of elements has no significant meaning.
The TRL is initialized as empty, i.e., the initial content of the TRL
resource representation MUST be an empty CBOR array.
4.1. Update of the TRL Resource
The Authorization Server updates the TRL in the following two cases.
* When a non-expired Access Token is revoked, the token hash of the
Access Token is added to the TRL resource representation. That
is, a CBOR byte string with the token hash as its value is added
to the CBOR array used as TRL resource representation.
* When a revoked Access Token expires, the token hash of the Access
Token is removed from the TRL resource representation. That is,
the CBOR byte string with the token hash as its value is removed
from the CBOR array used as TRL resource representation.
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5. The TRL Endpoint
Consistent with Section 6.5 of [I-D.ietf-ace-oauth-authz], all
communications between a caller of the TRL endpoint and the
Authorization Server MUST be encrypted, as well as integrity and
replay protected. Furthermore, responses from the Authorization
Server to the caller MUST be bound to the caller's request.
Following a request to the TRL endpoint, the messages defined in this
document that the Authorization Server sends as response use Content-
Format "application/ace-trl+cbor". Their payload is formatted as a
CBOR map, and the CBOR values for the parameters included therein are
defined in Section 12.
The Authorization Server MUST implement measures to prevent access to
the TRL endpoint by entities other than registered devices and
authorized administrators.
The TRL endpoint supports only the GET method, and allows two types
of query of the TRL.
* Full query: the Authorization Server returns the token hashes of
the revoked Access Tokens currently in the TRL and pertaining to
the requester.
The Authorization Server MUST support this type of query. The
processing of a full query and the related response format are
defined in Section 6.
* Diff query: the Authorization Server returns a list of diff
entries. Each diff entry is related to one of the most recent
updates, in the portion of the TRL pertaining to the requester.
The entry associated with one of such updates contains a list of
token hashes, such that: i) the corresponding revoked Access
Tokens pertain to the requester; and ii) they were added to or
removed from the TRL at that update.
The Authorization Server MAY support this type of query. In such
a case, the Authorization Server maintains the history of updates
to the TRL resource as defined in Section 5.1. The processing of
a diff query and the related response format are defined in
Section 7.
If it supports diff queries, the Authorization Server MAY
additionally support its "Cursor" extension, which has two benefits.
First, the Authorization Server can avoid excessively big latencies
when several diff entries have to be transferred, by delivering one
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adjacent subset at the time, in different diff query responses.
Second, a requester can retrieve diff entries associated with TRL
updates that, even if not the most recent ones, occurred after a TRL
update indicated as reference point.
If it supports the "Cursor" extension, the Authorization Server
stores additional information when maintaining the history of updates
to the TRL resource, as defined in Section 5.1.1. Also, the
processing of full query requests and diff query requests, as well as
the related response format, are further extended as defined in
Section 8.
5.1. Supporting Diff Queries
If the Authorization Server supports diff queries, it is able to
transfer a list of diff entries, as a series of TRL updates. That
is, when replying to a diff query performed by a requester, the
Authorization Server specifies the most recent updates to the portion
of the TRL pertaining to that requester.
The following defines how the Authorization Server builds and
maintains consistent histories of TRL updates for each registered
device and administrator, hereafter referred to as requesters.
For each requester, the Authorization Server maintains an update
collection of maximum N_MAX series items, where N_MAX is a pre-
defined positive integer. The Authorization Server MUST keep track
of the N_MAX most recent updates to the portion of the TRL that
pertains to each requester. The Authorization Server SHOULD provide
requesters with the value of N_MAX, upon their registration (see
Section 9).
The series items in the update collection MUST be strictly ordered in
a chronological fashion. That is, at any point in time, the current
first series item is the one least recently added to the update
collection and still retained by the Authorization Server, while the
current last series item is the one most recently added to the update
collection. The particular method used to achieve this is
implementation-specific.
Each time the TRL changes, the Authorization Server performs the
following operations for each requester.
1. The Authorization Server considers the portion of the TRL
pertaining to that requester. If the TRL portion is not affected
by this TRL update, the Authorization Server stops the processing
for that requester.
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2. Otherwise, the Authorization Server creates two sets "trl_patch"
of token hashes, i.e., one "removed" set and one "added" set, as
related to this TRL update.
3. The Authorization Server fills the two sets with the token hashes
of the removed and added Access Tokens, respectively, from/to the
TRL portion considered at step 1.
4. The Authorization Server creates a new series item, which
includes the two sets from step 3.
5. If the update collection associated with the requester currently
includes N_MAX series items, the Authorization Server MUST delete
the oldest series item in the update collection.
This occurs when the number of TRL updates pertaining to the
requester and currently stored at the Authorization Server is
equal to N_MAX.
6. The Authorization Server adds the series item to the update
collection associated with the requester, as the most recent one.
5.1.1. Supporting the "Cursor" Extension
If it supports the "Cursor" extension for diff queries, the
Authorization Server performs also the following actions.
When maintaining the history of updates to the TRL resource, the
following applies for each update collection.
* Each series item X in the update collection is also associated
with an unsigned integer 'index'. The value of 'index' is the
absolute counter of series items added to that update collection
until and including X, minus 1.
That is, the first series item ever added to that update
collection has 'index' with value 0. Also, after having added V
series item to the update collection, the last series item has
'index' with value (V - 1), independently of the maximum possible
size of the update collection (i.e., N_MAX).
* The unsigned integer LAST_INDEX is also defined. At every point
in time, the value of LAST_INDEX is the value of 'index' currently
associated with the latest added series item in the update
collection.
That is, the value of LAST_INDEX is the total number of series
items added so far to the update collection, minus 1.
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When processing a diff query using the "Cursor" extension, the values
of 'index' are used as cursor information, as defined in Section 8.2.
Furthermore, the Authorization Server defines an unsigned integer
MAX_DIFF_BATCH <= N_MAX. The value of MAX_DIFF_BATCH specifies the
maximum number of diff entries to be included in a single diff query
response. If supporting the "Cursor" extension, the Authorization
Server SHOULD provide registered devices and administrators with the
value of MAX_DIFF_BATCH, upon their registration (see Section 9).
5.2. Query Parameters
The TRL endpoint allows the following query parameters to be present
in a GET request. The Authorization Server MUST silently ignore
unknown query parameters.
* 'pmax': if included, it follows the semantics defined in
Section 3.2.2 of [I-D.ietf-core-conditional-attributes]. This
query parameter is relevant only in case the GET request is
specifically an Observation Request, i.e., if it includes the CoAP
Observe Option set to 0 (register). In such a case, this
parameter indicates the maximum time, in seconds, between two
consecutive notifications for the observation in question,
regardless whether the TRL resource has changed or not.
If the Observation Request does not include the 'pmax' parameter,
the maximum time to consider is up to the Authorization Server.
If the Observation Request includes the 'pmax' parameter, its
value MUST be greater than zero, otherwise the Authorization
Server MUST return a 4.00 (Bad Request) response.
If the GET request is not an Observation Request, the
Authorization Server MUST ignore the 'pmax' parameter, in case
this is included.
* 'diff': if included, it indicates to perform a diff query of the
TRL (see Section 7). Its value MUST be either:
- the integer 0, indicating that a (notification) response should
include as many diff entries as the Authorization Server can
provide in the response; or
- a positive integer greater than 0, indicating the maximum
number of diff entries that a (notification) response should
include.
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If the Authorization Server does not support diff queries, it
ignores the query parameter 'diff' when present in the GET request
and proceeds like when processing a full query of the TRL (see
Section 6).
Otherwise, the Authorization Server MUST return a 4.00 (Bad
Request) response in case the query parameter 'diff' of the GET
request specifies a value other than 0 or than a positive integer.
The response MUST have Content-Format "application/ace-trl+cbor".
The payload of the response is a CBOR map, which MUST include the
'error' field with value 0 ("Invalid parameter value") and MAY
include the 'error_description' field to provide additional
context.
* 'cursor': if included, it indicates to perform a diff query of the
TRL together with the "Cursor" extension, as defined in
Section 8.2. Its value MUST be either 0 or a positive integer.
If the Authorization Server does not support the "Cursor"
extension, it ignores the query parameter 'cursor' when present in
the GET request. In such a case, the Authorization Server
proceeds: i) like when processing a diff query of the TRL (see
Section 7), if it supports diff queries and the query parameter
'diff' is present in the GET request, or ii) like when processing
a full query of the TRL (see Section 6) otherwise.
If the Authorization Server supports both diff queries and the
"Cursor" extension, and the GET request specifies the query
parameter 'cursor', then the Authorization Server MUST return a
4.00 (Bad Request) response in case any of the following
conditions holds.
- The GET request does not specify the query parameter 'diff'.
The 'error' parameter within the CBOR map carried in the
response payload MUST have value 1 ("Invalid set of
parameters").
- The query parameter 'cursor' has a value other than 0 or than a
positive integer. The 'error' parameter within the CBOR map
carried in the response payload MUST have value 0 ("Invalid
parameter value").
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- The query parameter 'cursor' has a value strictly greater than
the current LAST_INDEX for the update collection associated
with the requester (see Section 5.1.1). The 'error' parameter
within the CBOR map carried in the response payload MUST have
value 2 ("Out of bound cursor value"). The CBOR map MUST also
include the 'cursor' parameter, which MUST specify the current
value of LAST_INDEX for the update collection associated with
the requester.
The 4.00 (Bad Request) response MUST have Content-Format
"application/ace-trl+cbor". The payload of the response MUST be a
CBOR map, which MUST include the 'error' parameter and MAY include
the 'error_description' parameter to provide additional context.
6. Full Query of the TRL
In order to produce a (notification) response to a GET request asking
for a full query of the TRL, the Authorization Server performs the
following actions.
1. From the current TRL resource representation, the Authorization
Server builds a set HASHES, such that:
* If the requester is a registered device, HASHES specifies the
token hashes of the Access Tokens pertaining to that
registered device. The Authorization Server can use the
authenticated identity of the registered device to perform the
necessary filtering on the TRL resource representation.
* If the requester is an administrator, HASHES specifies all the
token hashes in the current TRL resource representation.
2. The Authorization Server sends a 2.05 (Content) response to the
requester. The response MUST have Content-Format "application/
ace-trl+cbor". The payload of the response is a CBOR map, which
MUST be formatted as follows.
* The 'full_set' parameter MUST be included and specifies a CBOR
array 'full_set_value'. Each element of 'full_set_value'
specifies one of the token hashes from the set HASHES, encoded
as a CBOR byte string. If the set HASHES is empty, the
'full_set' parameter specifies the empty CBOR array.
The order of the token hashes in the CBOR array is irrelevant,
i.e., the CBOR array MUST be treated as a set in which the
order of elements has no significant meaning.
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* The 'cursor' parameter MUST be included if the Authorization
Server supports both the diff queries and the related "Cursor"
extension (see Section 5.1 and Section 5.1.1). Its value is
specified according to what is defined in Section 8.1, and
provides the requester with information for performing a
follow-up diff query using the "Cursor" extension (see
Section 8.2).
If the Authorization Server does not support both diff queries
and the "Cursor" extension, this parameter MUST NOT be
included. In case the requester does not support both diff
queries and the "Cursor" extension, it MUST silently ignore
the 'cursor' parameter if present.
Figure 4 provides the CDDL definition [RFC8610] of the CBOR array
'full_set_value' specified in the response from the Authorization
Server, as value of the 'full_set' parameter.
token_hash = bytes
full_set_value = [* token_hash]
Figure 4: CDDL definition of 'full_set_value'
Figure 5 shows an example of response from the Authorization Server,
following a full query request to the TRL endpoint. Full token
hashes are omitted for brevity.
2.05 Content
Content-Format: application/ace-trl+cbor
Payload:
{
"full_set" : [
h'01fa51cc ... ', h'01748190 ... '
]
}
Figure 5: Example of response following a Full Query request to
the TRL endpoint
7. Diff Query of the TRL
In order to produce a (notification) response to a GET request asking
for a diff query of the TRL, the Authorization Server performs the
following actions.
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1. The Authorization Server defines the positive integer NUM as
follows. If the value N specified in the query parameter 'diff'
in the GET request is equal to 0 or greater than the pre-defined
positive integer N_MAX (see Section 5.1), then NUM takes the
value of N_MAX. Otherwise, NUM takes N.
2. The Authorization Server determines U = min(NUM, SIZE), where
SIZE <= N_MAX is the number of TRL updates pertaining to the
requester and currently stored at the Authorization Server.
3. The Authorization Server prepares U diff entries. If U is equal
to 0 (e.g., because SIZE is equal to 0 at step 2), then no diff
entries are prepared.
The prepared diff entries are related to the U most recent TRL
updates pertaining to the requester, as maintained in the update
collection for that requester (see Section 5.1). In particular,
the first diff entry refers to the most recent of such updates,
the second diff entry refers to the second from last of such
updates, and so on.
Each diff entry is a CBOR array 'diff_entry', which includes the
following two elements.
* The first element is a CBOR array 'removed'. Each element of
the array is a CBOR byte string, with value the token hash of
an Access Token such that: it pertained to the requester; and
it was removed from the TRL during the update associated with
the diff entry.
* The second element is a CBOR array 'added'. Each element of
the array is a CBOR byte string, with value the token hash of
an Access Token such that: it pertains to the requester; and
it was added to the TRL during the update associated with the
diff entry.
The order of the token hashes in the CBOR arrays 'removed' and
'added' is irrelevant. That is, the CBOR arrays 'removed' and
'added' MUST be treated as a set in which the order of elements
has no significant meaning.
4. The Authorization Server prepares a 2.05 (Content) response for
the requester. The response MUST have Content-Format
"application/ace-trl+cbor". The payload of the response is a
CBOR map, which MUST be formatted as follows.
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* The 'diff_set' parameter MUST be present and specifies a CBOR
array 'diff_set_value' of U elements. Each element of
'diff_set_value' specifies one of the CBOR arrays 'diff_entry'
prepared above as diff entry. Note that U might have value 0,
in which case 'diff_set_value' is the empty CBOR array.
Within 'diff_set_value', the CBOR arrays 'diff_entry' MUST be
sorted to reflect the corresponding updates to the TRL in
reverse chronological order. That is, the first 'diff_entry'
element of 'diff_set_value' relates to the most recent update
to the portion of the TRL pertaining to the requester. The
second 'diff_entry' element relates to the second from last
most recent update to that portion, and so on.
* The 'cursor' parameter and the 'more' parameters MUST be
included if the Authorization Server supports both the diff
queries and the related "Cursor" extension (see
Section 5.1.1). Their values are specified according to what
is defined in Section 8.2, and provide the requester with
information for performing a follow-up query to the TRL
endpoint (see Section 8.2).
If the Authorization Server does not support both diff queries
and the "Cursor" extension, these parameters MUST NOT be
included. In case the requester does not support both diff
queries and the "Cursor" extension, it MUST silently ignore
the 'cursor' parameter and the 'more' parameter if present.
Figure 6 provides the CDDL definition [RFC8610] of the CBOR array
'diff_set_value' specified in the response from the Authorization
Server, as value of the 'diff_set' parameter.
token_hash = bytes
trl_patch = [* token_hash]
diff_entry = [removed: trl_patch, added: trl_patch]
diff_set_value = [* diff_entry]
Figure 6: CDDL definition of 'diff_set_value'
Figure 7 shows an example of response from the Authorization Server,
following a Diff Query request to the TRL endpoint, where U = 3 diff
entries are specified. Full token hashes are omitted for brevity.
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2.05 Content
Content-Format: application/ace-trl+cbor
Payload:
{
"diff_set" : [
[
[ h'01fa51cc ... ', h'01748190 ... '],
[ h'01cdf1ca ... ', h'01be41a6 ... ']
],
[
[ h'0144dd12 ... ', h'01231fff ... '],
[]
],
[
[],
[ h'01ca986f ... ', h'01fe1a2b ... ']
]
]
}
Figure 7: Example of response following a Diff Query request to
the TRL endpoint
Appendix A discusses how performing a diff query of the TRL is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
8. Using the "Cursor" Extension
If it supports both diff queries and the "Cursor" extension, the
Authorization Server composes a response to a full query request or
diff query request as defined in Section 8.1 and Section 8.2,
respectively.
The exact format of the response depends on the request being a full
query or diff query request, on the presence of the query parameter
'cursor' in the diff query request, and on the current status of the
update collection associated with the requester.
8.1. Response to Full Query
When processing a full query request to the TRL endpoint, the
Authorization Server composes a response as defined in Section 6.
In particular, the 'cursor' parameter included in the CBOR map
carried in the response payload specifies either the CBOR simple
value "null" (0xf6) or a CBOR unsigned integer.
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The 'cursor' parameter MUST specify the CBOR simple value "null" in
case there are currently no TRL updates pertinent to the requester,
i.e., the update collection for that requester is empty. This is the
case from when the requester registers at the Authorization Server
until a first update pertaining to that requester occurs to the TRL.
Otherwise, the 'cursor' parameter MUST specify a CBOR unsigned
integer. This MUST take the 'index' value of the last series item in
the update collection associated with the request (see
Section 5.1.1), as corresponding to the most recent update pertaining
to the requester occurred to the TRL.
8.2. Response to Diff Query
When processing a diff query request to the TRL endpoint, the
Authorization Server composes a response as defined in the following.
8.2.1. Empty Collection
If the update collection associated with the requester has no
elements, the Authorization Server returns a 2.05 (Content) response.
The response MUST have Content-Format "application/ace-trl+cbor" and
its payload MUST be a CBOR map formatted as follows.
* The 'diff_set' parameter MUST be included and specifies the empty
CBOR array.
* The 'cursor' parameter MUST be included and specifies the CBOR
simple value "null" (0xf6).
* The 'more' parameter MUST be included and specifies the CBOR
simple value "false" (0xf4).
Note that the above applies when the update collection associated
with the requester has no elements, regardeless whether the query
parameter 'cursor' is included or not in the diff query request.
8.2.2. Cursor Not Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request does not include the query parameter
'cursor', the Authorization Server performs the same actions defined
in Section 7, with the following differences.
* At step 3, the Authorization Server considers the value
MAX_DIFF_BATCH (see Section 5.1.1), and prepares L = min(U,
MAX_DIFF_BATCH) diff entries. If L is equal to 0 (e.g., because U
is equal to 0), then no diff entries are prepared.
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If U <= MAX_DIFF_BATCH, the prepared diff entries are the last
series items in the update collection associated with the
requester, corresponding to the L most recent TRL updates
pertaining to the requester.
If U > MAX_DIFF_BATCH, the prepared diff entries are the eldest of
the last U series items in the update collection associated with
the requester, as corresponding to the first L of the U most
recent TRL updates pertaining to the requester.
* At step 4, the CBOR map to carry in the payload of the 2.05
(Content) response MUST be formatted as follows.
- The 'diff_set' parameter MUST be present and specifies a CBOR
array 'diff_set_value' of L elements. Each element of
'diff_set_value' specifies one of the CBOR arrays 'diff_entry'
prepared as diff entry. Note that L might have value 0, in
which case 'diff_set_value' is the empty CBOR array.
- The 'cursor' parameter MUST be present and specifies a CBOR
unsigned integer. This MUST take the 'index' value of the
series item of the update collection included as first diff
entry in the 'diff_set_value' CBOR array, which is specified by
the 'diff_set' parameter. That is, the 'cursor' parameter
takes the 'index' value of the series item in the update
collection corresponding to the most recent update pertaining
to the requester and returned in this diff query response.
Note that the 'cursor' parameter takes the same 'index' value
of the last series item in the update collection when U <=
MAX_DIFF_BATCH.
- The 'more' parameter MUST be present and MUST specify the CBOR
simple value "false" (0xf4) if U <= MAX_DIFF_BATCH, or the CBOR
simple value "true" (0xf5) otherwise.
If the 'more' parameter has value "true", the requester can
send a follow-up diff query request including the query
parameter 'cursor', with the same value of the 'cursor'
parameter specified in this diff query response. As defined in
Section 8.2.3, this would result in the Authorization Server
transferring the following subset of series items as diff
entries, thus resuming from where interrupted in the previous
transfer.
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8.2.3. Cursor Specified in the Diff Query Request
If the update collection associated with the requester is not empty
and the diff query request includes the query parameter 'cursor' with
value P, the Authorization Server proceeds as follows, depending on
which of the following two cases hold.
* Case A - The series item X with 'index' having value P and the
series item Y with 'index' having value P+1 are both not found in
the update collection associated with the requester. This occurs
when the item Y (and possibly further ones after it) has been
previously removed from the history of updates for that requester
(see step 5 at Section 5.1).
In this case, the Authorization Server returns a 2.05 (Content)
response. The response MUST have Content-Format "application/ace-
trl+cbor" and its payload MUST be a CBOR map formatted as follows.
- The 'diff_set' parameter MUST be included and specifies the
empty CBOR array.
- The 'cursor' parameter MUST be included and specifies the CBOR
simple value "null" (0xf6).
- The 'more' parameter MUST be included and specifies the CBOR
simple value "true" (0xf5).
With the combination ('cursor', 'more') = ("null", "true"), the
Authorization Server is signaling that the update collection is in
fact not empty, but that one or more series items have been lost
due to their removal. These include the item with 'index' value
P+1, that the requester wished to obtain as the first one
following the specified reference point with 'index' value P.
When receiving this diff query response, the requester should send
a new full query request to the Authorization Server, in order to
fully retrieve the current pertaining portion of the TRL.
* Case B - The series item X with 'index' having value P is found in
the update collection associated with the requester; or the series
item X is not found and the series item Y with 'index' having
value P+1 is found in the update collection associated with the
requester.
In this case, the Authorization Server performs the same actions
defined in Section 7, with the following differences.
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- At step 3, the Authorization Server considers the value
MAX_DIFF_BATCH (see Section 5.1.1), and prepares L = min(SUB_U,
MAX_DIFF_BATCH) diff entries, where SUB_U = min(NUM, SUB_SIZE),
and SUB_SIZE is the number of series items in the update
collection following the series item X. If L is equal to 0
(e.g., because SUB_U is equal to 0), then no diff entries are
prepared.
If SUB_U <= MAX_DIFF_BATCH, the prepared diff entries are the
last series items in the update collection associated with the
requester, corresponding to the L most recent TRL updates
pertaining to the requester.
If SUB_U > MAX_DIFF_BATCH, the prepared diff entries are the
eldest of the last SUB_U series items in the update collection
associated with the requester, corresponding to the first L of
the SUB_U most recent TRL updates pertaining to the requester.
- At step 4, the CBOR map to carry in the payload of the 2.05
(Content) response MUST be formatted as follows.
o The 'diff_set' parameter MUST be present and specifies a
CBOR array 'diff_set_value' of L elements. Each element of
'diff_set_value' specifies one of the CBOR arrays
'diff_entry' prepared as diff entry. Note that L might have
value 0, in which case 'diff_set_value' is the empty CBOR
array.
o The 'cursor' parameter MUST be present and MUST specify a
CBOR unsigned integer. In particular:
+ If L is equal to 0, i.e., the series item X is the last
one in the update collection, then the 'cursor' parameter
MUST take the same 'index' value of the last series item
in the update collection.
+ If L is different than 0, then the 'cursor' parameter
MUST take the 'index' value of the series element of the
update collection included as first diff entry in the
'diff_set' CBOR array. That is, the 'cursor' parameter
takes the 'index' value of the series item in the update
collection corresponding to the most recent update
pertaining to the requester and returned in this diff
query response.
Note that the 'cursor' parameter takes the same 'index'
value of the last series item in the update collection when
SUB_U <= MAX_DIFF_BATCH.
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o The 'more' parameter MUST be present and MUST specify the
CBOR simple value "false" (0xf4) if SUB_U <= MAX_DIFF_BATCH,
or the CBOR simple value "true" (0xf5) otherwise.
If 'more' has value "true", the requester can send a follow-
up diff query request including the query parameter
'cursor', with the same value of the 'cursor' parameter
specified in this diff query response. This would result in
the Authorization Server transferring the following subset
of series items as diff entries, thus resuming from where
interrupted in the previous transfer.
9. Upon Registration
During the registration process at the Authorization Server, an
administrator or a registered device receives the following
information as part of the registration response.
* The url-path to the TRL endpoint at the Authorization Server.
* The hash function used to compute token hashes. This is specified
as an integer or a text string, taking value from the "ID" or
"Hash Name String" column of the "Named Information Hash
Algorithm" Registry [Named.Information.Hash.Algorithm],
respectively.
* Optionally, a positive integer N_MAX, if the Authorization Server
supports diff queries of the TRL resource (see Section 5.1 and
Section 7).
* Optionally, a positive integer MAX_DIFF_BATCH, if the
Authorization Server supports diff queries of the TRL resource as
well as the related "Cursor" extension (see Section 5.1.1 and
Section 8).
After the registration procedure is finished, the administrator or
registered device can send a GET request to the TRL resource,
including the CoAP Observe Option set to 0 (register), in order to
start an observation of the TRL resource at the Authorization Server
as per Section 3.1 of [RFC7641]. The GET request can express the
wish for a full query (see Section 6) or a diff query (see Section 7)
of the TRL.
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In case the request is successfully processed, the Authorization
Server replies with a response specifying the CoAP response code 2.05
(Content) and including the CoAP Observe Option. The payload of the
response is formatted as defined in Section 6 or in Section 7, in
case the GET request yielded the execution of a full query or a diff
query of the TRL, respectively.
Further details about the registration process at the Authorization
Server are out of scope for this specification. Note that the
registration process is also out of the scope of the ACE framework
for Authentication and Authorization (see Section 5.5 of
[I-D.ietf-ace-oauth-authz]).
10. Notification of Revoked Tokens
When the TRL is updated (see Section 4.1), the Authorization Server
sends Observe Notifications to the observers of the TRL resource.
Observe Notifications are sent as per Section 4.2 of [RFC7641].
If the 'pmax' query parameter was specified in the Observation
Request starting an observation (see Section 5.2), the Authorization
Server might accordingly send additional Observe Notifications to the
associated observer. That is, the Authorization Server ensures that
no more than pmax seconds elapse between two consecutive
notifications sent to that observer, regardless whether the TRL
resource has changed or not. If the 'pmax' query parameter was not
specified in the Observation Request, a possible maximum time to
consider is up to the Authorization Server.
The payload of each Observe Notification is formatted as defined in
Section 6 or in Section 7, in case the original Observation Request
yielded the execution of a full query or a diff query of the TRL,
respectively.
Furthermore, an administrator or a registered device can send
additional GET requests to the TRL endpoint at any time, in order to
retrieve the token hashes of the pertaining revoked Access Tokens.
When doing so, the caller of the TRL endpoint can perform a full
query (see Section 6) or a diff query (see Section 7) of the TRL.
When receiving a response from the TRL endpoint, a registered device
MUST expunge every stored Access Token associated with a token hash
specified in the response.
When a Resource Server RS receives a response from the TRL endpoint
specifying the token hash th1 associated with a revoked Access Token
t1, the RS might not have received and stored that Access Token yet.
This occurs if the Access Token is revoked before it is successfully
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posted to the Authorization Information Endpoint at the RS (see
Section 5.10.1 of [I-D.ietf-ace-oauth-authz]). Such a delay can be
due, for example, to messages that get lost in transmission, or
rather to the Client experiencing failures in sending the Access
Token to the RS, or deliberately holding the Access Token back.
Thus, in order to ensure that no revoked Access Tokens are accepted
and stored, the RS performs the following actions.
* The RS MUST store the token hash th1, until gaining knowledge that
the associated revoked Access Token t1 is also expired.
This can happen when receiving a subsequent response from the TRL
endpoint (i.e., indicating that the token hash th1 is not in the
TRL portion pertaining to the RS anymore), or when the Access
Token t1 is posted to the Authorization Information Endpoint and
is found to be expired based on its 'exp' claim [RFC7519], if
included.
* The RS MUST NOT accept as valid and store an Access Token t1
posted to the Authorization Information Endpoint, if the
corresponding token hash th1 is among the stored ones.
11. Interaction Examples
This section provides examples of interactions between a Resource
Server RS as a registered device and an Authorization Server AS. The
Authorization Server supports both full query and diff query of the
TRL, as defined in Section 6 and Section 7, respectively.
The details of the registration process are omitted, but it is
assumed that the Resource Server sends an unspecified payload to the
Authorization Server, which replies with a 2.01 (Created) response.
The payload of the registration response is a CBOR map, which
includes the following entries:
* a "trl_path" parameter, specifying the path of the TRL resource;
* a "trl_hash" parameter, specifying the hash function used to
computed token hashes as defined in Section 3;
* an "n_max" parameter, specifying the value of N_MAX, i.e., the
maximum number of TRL updates pertaining to each registered device
that the Authorization Server retains for that device (see
Section 7);
* possible further parameters related to the registration process.
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Furthermore, 'h(x)' refers to the hash function used to compute the
token hashes, as defined in Section 3 of this specification and
according to [RFC6920]. Assuming the usage of CWTs transported in
CBOR, 'bstr.h(t1)' and 'bstr.h(t2)' denote the byte-string
representations of the token hashes for the Access Tokens t1 and t2,
respectively.
11.1. Full Query with Observation
Figure 8 shows an interaction example considering a CoAP observation
and a full query of the TRL.
RS AS
| |
| Registration: POST |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "n_max" : 10 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl/ |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
| . |
| . |
| . |
| |
| (Access Tokens t1 and t2 issued |
| and successfully submitted to RS) |
| . |
| . |
| . |
| |
| |
| (Access Token t1 is revoked) |
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| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 53 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1)] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 is revoked) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1), bstr.h(t2)] |
| } |
| |
| . |
| . |
| . |
| |
| (Access Token t1 expires) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 expires) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
| |
Figure 8: Interaction for Full Query with Observation
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11.2. Diff Query with Observation
Figure 9 shows an interaction example considering a CoAP observation
and a diff query of the TRL.
The Resource Server indicates N=3 as value of the query parameter
'diff', i.e., as the maximum number of diff entries to be specified
in a response from the Authorization Server.
RS AS
| |
| Registration: POST |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "n_max" : 10 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl?diff=3 |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [] |
| } |
| . |
| . |
| . |
| |
| (Access Tokens t1 and t2 issued |
| and successfully submitted to RS) |
| . |
| . |
| . |
| |
| (Access Token t1 is revoked) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 53 |
| Content-Format: "application/ace-trl+cbor" |
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| Payload: { |
| "diff_set" : [ |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 is revoked) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| . |
| . |
| . |
| |
| (Access Token t1 expires) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 expires) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
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| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ] |
| ] |
| } |
| |
Figure 9: Interaction for Diff Query with Observation
11.3. Full Query with Observation and Additional Diff Query
Figure 10 shows an interaction example considering a CoAP observation
and a full query of the TRL.
The example also considers one of the notifications from the
Authorization Server to get lost in transmission, and thus not
reaching the Resource Server.
When this happens, and after a waiting time defined by the
application has elapsed, the Resource Server sends a GET request with
no Observe Option to the Authorization Server, to perform a diff
query of the TRL. The Resource Server indicates N=8 as value of the
query parameter 'diff', i.e., as the maximum number of diff entries
to be specified in a response from the Authorization Server.
RS AS
| |
| Registration: POST |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.01 CREATED |
| Payload: { |
| ... |
| "trl_path" : "revoke/trl", |
| "trl_hash" : "sha-256", |
| "n_max" : 10 |
| } |
| |
| GET Observe: 0 |
| coap://as.example.com/revoke/trl/ |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 42 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
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| . |
| . |
| . |
| |
| (Access Tokens t1 and t2 issued |
| and successfully submitted to RS) |
| . |
| . |
| . |
| |
| (Access Token t1 is revoked) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 53 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1)] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 is revoked) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 64 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t1), bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access Token t1 expires) |
| |
|<--------------------------------------------------+
| 2.05 CONTENT Observe: 75 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [bstr.h(t2)] |
| } |
| . |
| . |
| . |
| |
| (Access Token t2 expires) |
| |
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| X<---------------------------------------------+
| 2.05 CONTENT Observe: 86 |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "full_set" : [] |
| } |
| . |
| . |
| . |
| |
| (Enough time has passed since |
| the latest received notification) |
| |
| GET |
| coap://as.example.com/revoke/trl?diff=8 |
+-------------------------------------------------->|
| |
|<--------------------------------------------------+
| 2.05 CONTENT |
| Content-Format: "application/ace-trl+cbor" |
| Payload: { |
| "diff_set" : [ |
| [ [bstr.h(t2)], [] ], |
| [ [bstr.h(t1)], [] ], |
| [ [], [bstr.h(t2)] ], |
| [ [], [bstr.h(t1)] ] |
| ] |
| } |
| |
Figure 10: Interaction for Full Query with Observation and Diff Query
12. ACE Token Revocation List Parameters
This specification defines a number of parameters that can be
transported in the response from the TRL endpoint, when the response
payload is a CBOR map. Note that such a response MUST use the
Content-Format "application/ace-trl+cbor" defined in Section 15.2 of
this specification.
The table below summarizes them, and specifies the CBOR value to use
as abbreviation instead of the full descriptive name.
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+-------------------+------------+------------------------+
| Name | CBOR Value | CBOR Type |
+-------------------+------------+------------------------+
| full_set | 0 | array |
+-------------------+------------+------------------------+
| diff_set | 1 | array |
+-------------------+------------+------------------------+
| cursor | 2 | unsigned integer / |
| | | simple value "null" |
+-------------------+------------+------------------------+
| more | 3 | simple value "false" / |
| | | simple value "true" |
+-------------------+------------+------------------------+
| error | -1 | int |
+-------------------+------------+------------------------+
| error_description | -2 | tstr |
+-------------------+------------+------------------------+
Figure 11: CBOR abbreviations for the ACE Token Revocation List
parameters
13. ACE Token Revocation List Error Identifiers
This specification defines a number of values that the Authorization
Server can include as error identifiers, in the 'error' field of an
error response from the TRL endpoint. This applies to error
responses whose payload is a CBOR map and whose Content-Format is
"application/ace-trl+cbor".
+-------+---------------------------+
| Value | Description |
+-------+---------------------------+
| 0 | Invalid parameter value |
+-------+---------------------------+
| 1 | Invalid set of parameters |
+-------+---------------------------+
| 2 | Out of bound cursor value |
+-------+---------------------------+
Figure 12: ACE Token Revocation List Error Identifiers
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14. Security Considerations
Security considerations are inherited from the ACE framework for
Authentication and Authorization [I-D.ietf-ace-oauth-authz], from
[RFC8392] as to the usage of CWTs, from [RFC7519] as to the usage of
JWTs, from [RFC7641] as to the usage of CoAP Observe, and from
[RFC6920] with regard to resource naming through hashes. The
following considerations also apply.
The Authorization Server MUST ensure that each registered device can
access and retrieve only its pertaining portion of the TRL. To this
end, the Authorization Server can perform the required filtering
based on the authenticated identity of the registered device, i.e., a
(non-public) identifier that the Authorization Server can securely
relate to the registered device and the secure association that they
use to communicate.
Disclosing any information about revoked Access Tokens to entities
other than the intended registered devices may result in privacy
concerns. Therefore, the Authorization Server MUST ensure that,
other than registered devices accessing their own pertaining portion
of the TRL, only authorized and authenticated administrators can
retrieve the full TRL. To this end, the Authorization Server may
rely on an access control list or similar.
If a registered device has many non-expired Access Tokens associated
with itself that are revoked, the pertaining portion of the TRL could
grow to a size bigger than what the registered device is prepared to
handle upon reception, especially if relying on a full query of the
TRL resource (see Section 6). This could be exploited by attackers
to negatively affect the behavior of a registered device. Issuing
Access Tokens with not too long expiration time could help reduce the
size of a TRL, but an Authorization Server SHOULD take measures to
limit this size.
Most of the communication about revoked Access Tokens presented in
this specification relies on CoAP Observe Notifications sent from the
Authorization Server to a registered device. The suppression of
those notifications by an external attacker that has access to the
network would prevent registered devices from ever knowing that their
pertaining Access Tokens have been revoked. In order to avoid this,
a registered device SHOULD NOT rely solely on the CoAP Observe
notifications. In particular, a registered device SHOULD also
regularly poll the Authorization Server for the most current
information about revoked Access Tokens, by sending GET requests to
the TRL endpoint according to a related application policy.
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15. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
15.1. Media Type Registrations
IANA is asked to register the media type "application/ace-trl+cbor"
for messages of the protocols defined in this document encoded in
CBOR. This registration follows the procedures specified in
[RFC6838].
Type name: application
Subtype name: ace-trl+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: Must be encoded as CBOR map containing the
protocol parameters defined in [RFC-XXXX].
Security considerations: See Section 14 of this document.
Interoperability considerations: N/A
Published specification: [RFC-XXXX]
Applications that use this media type: The type is used by
Authorization Servers, Clients and Resource Servers that support the
notification of revoked Access Tokens, according to a Token
Revocation List maintained by the Authorization Server as specified
in [RFC-XXXX].
Fragment identifier considerations: N/A
Additional information: N/A
Person & email address to contact for further information:
<iesg@ietf.org>
Intended usage: COMMON
Restrictions on usage: None
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Author: Marco Tiloca <marco.tiloca@ri.se>
Change controller: IESG
15.2. CoAP Content-Formats Registry
IANA is asked to add the following entry to the "CoAP Content-
Formats" registry within the "CoRE Parameters" registry group.
Media Type: application/ace-trl+cbor
Encoding: -
ID: TBD
Reference: [RFC-XXXX]
15.3. ACE Token Revocation List Parameters Registry
This specification establishes the "ACE Token Revocation List
Parameters" IANA registry. The registry has been created to use the
"Expert Review" registration procedure [RFC8126]. Expert Review
guidelines are provided in Section 15.5. It should be noted that, in
addition to the Expert Review, some portions of the registry require
a specification, potentially a Standards Track RFC, to be supplied as
well.
The columns of this registry are:
* Name: This is a descriptive name that enables easier reference to
the item. The name MUST be unique. It is not used in the
encoding.
* CBOR Value: This is the value used as CBOR abbreviation of the
item. These values MUST be unique. The value can be a positive
integer or a negative integer. Different ranges of values use
different registration policies [RFC8126]. Integer values from
-256 to 255 are designated as Standards Action. Integer values
from -65536 to -257 and from 256 to 65535 are designated as
Specification Required. Integer values greater than 65535 are
designated as Expert Review. Integer values less than -65536 are
marked as Private Use.
* CBOR Type: This contains the CBOR type of the item, or a pointer
to the registry that defines its type, when that depends on
another item.
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* Reference: This contains a pointer to the public specification for
the item.
This registry has been initially populated by the values in
Section 12. The "Reference" column for all of these entries refers
to this document.
15.4. ACE Token Revocation List Errors
This specification establishes the "ACE Token Revocation List Errors"
IANA registry. The registry has been created to use the "Expert
Review" registration procedure [RFC8126]. Expert Review guidelines
are provided in Section 15.5. It should be noted that, in addition
to the Expert Review, some portions of the registry require a
specification, potentially a Standards Track RFC, to be supplied as
well.
The columns of this registry are:
* Value: The value to be used to identify the error. The value MUST
be unique. The value can be a positive integer or a negative
integer. Integer values between 0 and 255 are designated as
Standards Track Document required. Integer values from 256 to
65535 are designated as Specification Required. Integer values
greater than 65535 are designated as Expert Review. Integer
values less than -65536 are marked as private use.
* Description: This field contains a brief description of the error.
* Reference: This field contains a pointer to the public
specification defining the error, if one exists.
This registry has been initially populated by the values in
Section 13. The "Reference" column for all of these entries refers
to this document.
15.5. Expert Review Instructions
The IANA registries established in this document is defined as Expert
Review. This section gives some general guidelines for what the
experts should be looking for, but they are being designated as
experts for a reason so they should be given substantial latitude.
Expert reviewers should take into consideration the following points:
* Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already
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registered and that the point is likely to be used in deployments.
The zones tagged as private use are intended for testing purposes
and closed environments. Code points in other ranges should not
be assigned for testing.
* Specifications are required for the Standards Track range of point
assignment. Specifications should exist for Specification
Required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are
needed for the Expert Review range if they are expected to be used
outside of closed environments in an interoperable way. When
specifications are not provided, the description provided needs to
have sufficient information to identify what the point is being
used for.
* Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for
Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The
length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that
size.
16. References
16.1. Normative References
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", Work in Progress, Internet-Draft,
draft-ietf-ace-oauth-authz-46, 8 November 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oauth-
authz-46.txt>.
[I-D.ietf-core-conditional-attributes]
Koster, M., Soloway, A., and B. Silverajan, "Conditional
Attributes for Constrained RESTful Environments", Work in
Progress, Internet-Draft, draft-ietf-core-conditional-
attributes-04, 10 May 2022,
<https://www.ietf.org/archive/id/draft-ietf-core-
conditional-attributes-04.txt>.
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[Named.Information.Hash.Algorithm]
IANA, "Named Information Hash Algorithm",
<https://www.iana.org/assignments/named-information/named-
information.xhtml>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
Keranen, A., and P. Hallam-Baker, "Naming Things with
Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
<https://www.rfc-editor.org/info/rfc6920>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/info/rfc8610>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
16.2. Informative References
[I-D.bormann-t2trg-stp]
Bormann, C. and K. Hartke, "The Series Transfer Pattern
(STP)", Work in Progress, Internet-Draft, draft-bormann-
t2trg-stp-03, 7 April 2020,
<https://www.ietf.org/archive/id/draft-bormann-t2trg-stp-
03.txt>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <https://www.rfc-editor.org/info/rfc7009>.
Appendix A. On using the Series Transfer Pattern
Performing a diff query of the TRL as specified in Section 7 is in
fact a usage example of the Series Transfer Pattern defined in
[I-D.bormann-t2trg-stp].
That is, a diff query enables the transfer of a series of TRL
updates, with the Authorization Server specifying U <= N_MAX diff
entries as the U most recent updates to the portion of the TRL
pertaining to a requester, i.e., a registered device or an
administrator.
When responding to a diff query request from a requester (see
Section 7), 'diff_set' is a subset of the update collection
associated with the requester, where each 'diff_entry' record is a
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series item from that update collection. Note that 'diff_set'
specifies the whole current update collection when the value of U is
equal to SIZE, i.e., the current number of series items in the update
collection.
The value N of the query parameter 'diff' in the GET request allows
the requester and the Authorization Server to trade the amount of
provided information with the latency of the information transfer.
Since the update collection associated with each requester includes
up to N_MAX series item, the Authorization Server deletes the oldest
series item when a new one is generated and added to the end of the
update collection, due to a new TRL update pertaining to that
requester (see Section 5.1). This addresses the question "When can
the server decide to no longer retain older items?" raised in
Section 3.2 of [I-D.bormann-t2trg-stp].
Furthermore, performing a diff query of the TRL together with the
"Cursor" extension as specified in Section 8 in fact relies on the
"Cursor" pattern of the Series Transfer Pattern (see Section 3.3 of
[I-D.bormann-t2trg-stp]).
Appendix B. Document Updates
RFC EDITOR: Please remove this section.
B.1. Version -01 to -02
* Earlier mentioning of error cases.
* Clearer distinction between maintaining the history of TRL updates
and preparing the response to a diff query.
* Defined the use of "cursor" in the document body, as an extension
of diff queries.
* Both success and error responses have a CBOR map as payload.
* Corner cases of message processing explained more explcitly.
* Clarifications and editorial improvements.
B.2. Version -00 to -01
* Added actions to perform upon receiving responses from the TRL
endpoint.
* Fixed off-by-one error when using the "Cursor" pattern.
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* Improved error handling, with registered error codes.
* Section restructuring (full- and diff-query as self-standing
sections).
* Renamed identifiers and CBOR parameters.
* Clarifications and editorial improvements.
Acknowledgments
The authors sincerely thank Christian Amsüss, Carsten Bormann,
Benjamin Kaduk, David Navarro, Marco Rasori, Michael Richardson, Jim
Schaad, Göran Selander and Travis Spencer for their comments and
feedback.
The work on this document has been partly supported by VINNOVA and
the Celtic-Next project CRITISEC; and by the H2020 project SIFIS-Home
(Grant agreement 952652).
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Kista
Sweden
Email: marco.tiloca@ri.se
Ludwig Seitz
Combitech
Djaeknegatan 31
SE-21135 Malmoe
Sweden
Email: ludwig.seitz@combitech.com
Francesca Palombini
Ericsson AB
Torshamnsgatan 23
SE-16440 Kista
Sweden
Email: francesca.palombini@ericsson.com
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Sebastian Echeverria
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: secheverria@sei.cmu.edu
Grace Lewis
CMU SEI
4500 Fifth Avenue
Pittsburgh, PA, 15213-2612
United States of America
Email: glewis@sei.cmu.edu
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