TRAM T. Reddy
Internet-Draft S. Nandakumar
Intended status: Standards Track D. Wing
Expires: March 19, 2016 Cisco
B. Williams
Akamai, Inc.
September 16, 2015
Metadata discovery for third party authorized TURN session
draft-reddy-tram-token-metadata-01
Abstract
The operator of the TURN server might want to have fine grained
control on the clients usage of the server resources for providing
features such as limiting the bandwidth usage, number of allocations
and so on. This document proposes a generic mechanism for the
operator to introspect the access token to retrieve any policy
restrictions imposed by the authorization server on the TURN server
resources assigned to the client.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on March 19, 2016.
Copyright Notice
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Introspection Request . . . . . . . . . . . . . . . . . . . . 3
4. Introspection Response . . . . . . . . . . . . . . . . . . . 4
5. INTROSPECTION_ENDPOINT Attribute . . . . . . . . . . . . . . 5
6. Notifications from Introspection Endpoint . . . . . . . . . . 5
7. Example usage with WebRTC . . . . . . . . . . . . . . . . . . 6
8. Alternate Approach . . . . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10.1. JSON Web Token Claims . . . . . . . . . . . . . . . . . 9
10.2. Well-Known 'introspection' URI . . . . . . . . . . . . . 10
10.3. STUN attribute . . . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The TURN protocol [RFC5766] is used to setup a relay service (via a
TURN Server) to exchange traffic (real time media, data) between
peers when direct peer-to-peer connection is not otherwise possible.
Due to the costs associated with operating a relay service, it is
important to constrain resource usage. For example, the operator
might want to limit the number of allocations or bandwidth.
[RFC7635] allows clients to obtain OAuth2.0 access token (of type
'Assertion') authorized by a Authorization Server to access a given
TURN server. On receiving such a token, the TURN server validates
the token to grant or reject access to the session resources.
However, having a token doesn't provide any control for the operator
of the TURN server restrict the server's resources. This
specification proposes using the mechanism defined in
[I-D.ietf-oauth-introspection] to query OAuth2.0 authorization server
to determine resource restrictions for this token.
The rest of the document is organized as follows. Section 3 provides
procedure for querying the OAuth2.0 Introspection Endpoint and
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Section 4 shows the introspection response with the parameters
identifying the policy controls associated with the access token.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This document defines the following terms:
Access Token: OAuth 2.0 access token.
Token Introspection: The act of inquiring about the current state of
an OAuth 2.0 token through use of the network protocol defined in
this document.
Introspection Endpoint: The OAuth 2.0 endpoint through which the
token introspection operation is accomplished. The Introspection
Endpoint could be a WebRTC server.
3. Introspection Request
For introspecting the meta-information associated with the access
token, the TURN server shall execute the procedures defined in
Section 2.1 of [I-D.ietf-oauth-introspection].
POST {scheme}://{host}:{port}/.well-known/introspection
Accept: application/json
Content-Type: application/x-www-form-urlencoded
{
"token" : "string"
"token_type_hint" : "string"
}
token REQUIRED. This parameter is defined in
[I-D.ietf-oauth-introspection]. The access token is conveyed by
the TURN client to the TURN server as discussed in Section 3.1
of [RFC7635].
token_type_hint OPTIONAL. This parameter is defined in
[I-D.ietf-oauth-introspection]. The token type MUST be set to
'access_token' defined in [RFC7009]. If the token type is not
'access_token', the server rejects the request with a 400 (Bad
Request) error.
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Following is a non-normative example request showcasing the
introspection request for a given access token.
POST /introspect HTTP/1.1
Host: server.example.com
Accept: application/json
Content-Type: application/x-www-form-urlencoded
{
"token" : "2YotnFZFEjr1zCsicMWpAA"
"token_type_hint" : "access_token"
}
4. Introspection Response
The OAuth2.0 Introspection Endpoint on recognizing the token,
responds with a JSON object [RFC7159] in "application/json" format
with the following members.
HTTP/1.1 200 OK
Content-Type: application/json
{
"active" : "boolean",
"scope" : "string",
"max_upstream_bandwidth" : "unsigned integer",
"max_downstream_bandwidth" : "unsigned integer",
"max_allocations" : "unsigned integer",
"lifetime" : "unsigned integer",
}
active REQUIRED. This parameter is defined in
[I-D.ietf-oauth-introspection].
scope OPTIONAL. This parameter is defined in
[I-D.ietf-oauth-introspection]. For this specification, the
scope MUST be 'stun'.
max_upstream_bandwidth REQUIRED. The value of this parameter is
an 64 bit unsigned integer that represents the maximum upstream
bandwidth permitted for the token in kilobits per second (1
kilobit = 1024 bits).
max_downstream bandwidth REQUIRED. The value of this parameter
is an 64 bit unsigned integer that represents the maximum
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downstream bandwidth permitted for the token in kilobits per
second (1 kilobit = 1024 bits).
max_allocations: REQUIRED. 16 bit unsigned integer defining
maximum number of allocations that is allowable for the given
access token.
lifetime: REQUIRED: The lifetime of the access token, in
seconds.
NOTE: Future specifications are allowed to define further top-level
members as mandated by the use-cases.
Following is a non-normative example response:
HTTP/1.1 200 OK
Content-Type: application/json
{
"active" : true,
"scope" : "stun",
"upstream-bandwidth" : 4096,
"downstream-bandwidth" : 4096,
"max-allocations" : 1,
}
5. INTROSPECTION_ENDPOINT Attribute
This attribute is used by the TURN client to inform the TURN server
the FQDN of Introspection Endpoint.
The TURN server establishes an HTTPS connection with the indicated
server and sends the above-described communications to that server.
The INTROSPECTION_ENDPOINT attribute is a comprehension-optional
attribute (see Section 15 from [RFC5389]).
TBD: An alternate approach is to convey the FQDN in the token itself.
6. Notifications from Introspection Endpoint
Introspection Endpoint can send unsolicited responses to notify
updates to the metadata associated with the token to the TURN server
using HTTP/2 server push mechanism. Examples where such
notifications are desired are:
o The Introspection Endpoint can signal the TURN server to revoke
the access token after the call is terminated by setting lifetime
to zero.
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o When the call switches from audio to video, the Introspection
Endpoint notifies the increased bandwidth to the TURN server.
7. Example usage with WebRTC
Below diagram shows a flow where a WebRTC client uses the procedures
discussed in [RFC7635] to obtain a OAuth 2.0 access token from the
WebRTC server. The TURN Server queries the Introspection Endpoint to
determine the metadata associated with the token. Steps 7, 8 and 9
are done using the procedures mentioned in this document.
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+-------------------+ +--------+ +---------------+
| ......... TURN | | TURN | | WebRTC Server|
| .WebRTC . Client | | | | |
| .Client . | | Server | |(Introspection |
| ......... | | | | Endpoint) |
+-------------------+ +--------+ +---------------+
| | (1)Allocate request | |
| |----------------------------------------->| |
| | | |
| | (2)Allocate error response | |
| | (401 Unauthorized) | |
| |<-----------------------------------------| |
| | THIRD-PARTY-AUTHORIZATION | |
| | | |
| | | |
| | (3)HTTP Request for token | |
|-------------------------------------------------------------------->|
| |(4) HTTP Response with token parameters | |
|<--------------------------------------------------------------------|
|OAuth 2.0 | |
Attributes | |
|------>| | |
| | (5)Allocate request ACCESS-TOKEN | |
| |----------------------------------------->| |
| | | |
| | (6)Allocate success response | |
| |<-----------------------------------------| |
| | |(7)Introspection |
| | | Request |
| | |----------------->|
| | | |
| | |(8)Introspection |
| | | response |
| | |<-----------------|
| |<---------------------------------------->| |
| | TURN Messages | |
| | ////// integrity protected ////// | |
| | ////// integrity protected ////// | |
| | | (9)Introspection |
| | | response |
| | |<-----------------|
Figure 1: Metadata discovery for TURN session
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8. Alternate Approach
An alternate approach considered by the authors makes use of the
access token itself to deliver metadata related to the TURN
authentication request. Standard STUN TLV encoded attributes are
used to communicate additional metadata associated with the token.
Such attributes can be used to define the maximum bandwidth
utilization allowed for allocations associated with the token, the
maximum number of distinct concurrent allocations, etc.
To include STUN attributes within the body of the access token, the
authorization server simply appends them to the access token's
plaintext immediately after the lifetime field. The variable length
list of attributes MUST consume all of the additional plaintext data
space within the body of the access token. No explicit option length
value is required or provided.
In order for inclusion of attributes within the plaintext to work
correctly in the absence of an explicit length field, one of two
things must be true: either the receiver must be able to reliably
determine the correct content length from the output of the
decryption operation, or the receiver must be able to reliably
differentiate between padding bytes and data bytes within the token.
AES-128-GCM is an example of the first case, and AEAD mode AES-CBC-
HMAC-SHA256 is an example of the second case.
Before parsing the optional data within the access token, the TURN
server MUST first perform all token validation required by [RFC7635].
If any of the specified validation checks fail, the TURN server MUST
NOT attempt to parse optional attributes.
To interpret the optional attributes within an access token, the TURN
server first calculates the amount of option space included in the
plaintext by subtracting the size of the base payload data (14 bytes
+ key_length) from the total payload size. It then interprets the
data in the option space as STUN TLV formatted attributes. While
parsing the option space, the TURN server MUST apply the same
validations to the access token's attributes that it would have
applied if the attributes had been included in the outer STUN header
(e.g. Verify the data format and value types). If any such
validation checks fail, the TURN server MUST reject the STUN request
with an error response 401 (Unauthorized).
The following STUN attributes are defined by this document for
inclusion in the access token: TBD. Additional attributes may be
defined for this purpose in future specifications.
The primary benefits of this method of metadata distribution are:
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o It does not impose additional requirements on the Introspection
Endpoint for out of band communication with the TURN server.
o Communicating with the Introspection Endpoint may increase the
latency associated with TURN allocation request handling.
The primary shortcomings of this method of metadata distribution are:
o Needs a larger TURN packet to accommodate the token. For example,
inclusion of the four fields defined above
(max_upstream_bandwidth, max_downstream_bandwidth,
max_allocations, and lifetime) would increase the token size by
around 38 bytes, depending upon whether the AEAD algorithm
requires padding.
o The Introspection Endpoint cannot notify the TURN server of
changes to the metadata associated with the token.
[NOTE: Backward compatibility with [RFC7635] requires discussion, but
it should not be a major issue if the dynamic option space
calculation method described is considered acceptable.]
[NOTE: The authors are seeking feedback from the working group on the
relative merits of this approach versus the "Introspection Endpoint"
approach. Which should we attempt to move forward? Or does each one
have enough merit that we should try to advance both?]
9. Security Considerations
The Security Considerations and Privacy Considerations of
[I-D.ietf-oauth-introspection] apply to this document.
10. IANA Considerations
10.1. JSON Web Token Claims
This specification requests IANA to register the following values
into the IANA JSON Web Token Claims registry for JWT Claim Names.
o Claim Name: "max_upstream_bandwidth"
o Claim Description: Maximum limit of upstream bandwidth
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this document ]].
o Claim Name: "max_downstream_bandwidth"
o Claim Description: Maximum limit of downstream bandwidth
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this document ]].
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o Claim Name: "max_allocations"
o Claim Description: Maximum number of allocations
o Change Controller: IESG
o Specification Document(s): Section 4 of [[ this document ]].
10.2. Well-Known 'introspection' URI
This memo registers the 'introspection' well-known URI in the Well-
Known URIs registry as defined by [RFC5785].
URI suffix: introspection
Change controller: IETF
Specification document(s): This document
Related information: None
10.3. STUN attribute
[Paragraphs below in braces should be removed by the RFC Editor upon
publication]
[IANA is requested to add the following attributes to the STUN
attribute registry [iana-stun], the INTROSPECTION_ENDPOINT attribute
requires that IANA allocate a value in the "STUN attributes Registry"
from the comprehension-optional range (0x8000-0xBFFF)].
This document defines the INTROSPECTION_ENDPOINT attribute, described
in Section 5. IANA has allocated the comprehension-optional
codepoint TBD for this attribute.
11. Acknowledgements
Authors would like to thank Ram Mohan for comments and review.
12. References
12.1. Normative References
[I-D.ietf-oauth-introspection]
Richer, J., "OAuth 2.0 Token Introspection", draft-ietf-
oauth-introspection-11 (work in progress), July 2015.
[iana-stun]
IANA, , "IANA: STUN Attributes", April 2011,
<http://www.iana.org/assignments/stun-parameters/stun-pa
rameters.xml>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008,
<http://www.rfc-editor.org/info/rfc5389>.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010,
<http://www.rfc-editor.org/info/rfc5766>.
[RFC7635] Reddy, T., Patil, P., Ravindranath, R., and J. Uberti,
"Session Traversal Utilities for NAT (STUN) Extension for
Third-Party Authorization", RFC 7635,
DOI 10.17487/RFC7635, August 2015,
<http://www.rfc-editor.org/info/rfc7635>.
12.2. Informative References
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010,
<http://www.rfc-editor.org/info/rfc5785>.
[RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth
2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009,
August 2013, <http://www.rfc-editor.org/info/rfc7009>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
Authors' Addresses
Tirumaleswar Reddy
Cisco Systems, Inc.
Email: tireddy@cisco.com
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Suhas Nandakumar
Cisco Systems, Inc.
Email: snandaku@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Brandon Williams
Akamai, Inc.
8 Cambridge Center
Cambridge, MA 02142
USA
Email: brandon.williams@akamai.com
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