Transaction Tokens
draft-ietf-oauth-transaction-tokens-01
| Document | Type | Active Internet-Draft (oauth WG) | |
|---|---|---|---|
| Authors | Atul Tulshibagwale , George Fletcher , Pieter Kasselman | ||
| Last updated | 2024-03-16 | ||
| Replaces | draft-oauth-transaction-tokens | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-oauth-transaction-tokens-01
oauth A. Tulshibagwale
Internet-Draft SGNL
Intended status: Informational G. Fletcher
Expires: 17 September 2024 Capital One
P. Kasselman
Microsoft
16 March 2024
Transaction Tokens
draft-ietf-oauth-transaction-tokens-01
Abstract
Transaction Tokens (Txn-Tokens) enable workloads in a trusted domain
to ensure that user identity and authorization context of an external
programmatic request, such as an API invocation, are preserved and
available to all workloads that are invoked as part of processing
such a request. Txn-Tokens also enable workloads within the trusted
domain to optionally immutably assert to downstream workloads that
they were invoked in the call chain of the request.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Web Authorization
Protocol Working Group mailing list (oauth@ietf.org), which is
archived at https://mailarchive.ietf.org/arch/browse/oauth/.
Source for this draft and an issue tracker can be found at
https://github.com/oauth-wg/oauth-transaction-tokens.
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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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 17 September 2024.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. What are Transaction Tokens? . . . . . . . . . . . . . . 4
2.2. Creating Txn-Tokens . . . . . . . . . . . . . . . . . . . 4
2.2.1. Initial Creation . . . . . . . . . . . . . . . . . . 4
2.2.2. Replacement Txn-Tokens . . . . . . . . . . . . . . . 5
2.3. Txn-Token Lifetime . . . . . . . . . . . . . . . . . . . 5
2.4. Benefits of Txn-Tokens . . . . . . . . . . . . . . . . . 5
2.5. Txn-Token Issuance and Usage Flows . . . . . . . . . . . 5
2.5.1. Basic Flow . . . . . . . . . . . . . . . . . . . . . 5
2.5.2. Replacement Txn-Token Flow . . . . . . . . . . . . . 7
3. Notational Conventions . . . . . . . . . . . . . . . . . . . 8
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Txn-Token Format . . . . . . . . . . . . . . . . . . . . . . 9
5.1. JWT Header . . . . . . . . . . . . . . . . . . . . . . . 9
5.2. JWT Body Claims . . . . . . . . . . . . . . . . . . . . . 9
5.2.1. Requester Context . . . . . . . . . . . . . . . . . . 10
5.2.2. Example . . . . . . . . . . . . . . . . . . . . . . . 11
6. Txn-Token Service . . . . . . . . . . . . . . . . . . . . . . 12
7. Requesting Txn-Tokens . . . . . . . . . . . . . . . . . . . . 12
7.1. Txn-Token Request . . . . . . . . . . . . . . . . . . . . 13
7.2. Txn-Token Request Processing . . . . . . . . . . . . . . 14
7.3. Txn-Token Response . . . . . . . . . . . . . . . . . . . 15
7.4. Creating Replacement Txn-Tokens . . . . . . . . . . . . . 16
7.4.1. Txn-Token Service Responsibilities . . . . . . . . . 16
7.4.2. Replacement Txn-Token Request . . . . . . . . . . . . 16
7.4.3. Replacement Txn-Token Response . . . . . . . . . . . 16
7.5. Mutual Authentication of the Txn-Token Request . . . . . 16
8. Using Txn-Tokens . . . . . . . . . . . . . . . . . . . . . . 17
8.1. Txn-Token HTTP Header . . . . . . . . . . . . . . . . . . 17
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9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9.1. Txn-Token Lifetime . . . . . . . . . . . . . . . . . . . 17
9.2. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 18
9.3. Client Authentication . . . . . . . . . . . . . . . . . . 18
10. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
10.1. Obsfucation of Personal Information . . . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
11.1. OAuth Registry Contents . . . . . . . . . . . . . . . . 19
11.2. JWT Registry Contents . . . . . . . . . . . . . . . . . 19
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 21
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
Modern computing architectures often use multiple independently
running components called workloads. In many cases, external
invocations through externally visible interfaces such as APIs result
in a number of internal workloads being invoked in order to process
the external invocation. These workloads often run in virtually or
physically isolated networks. These networks and the workloads
running within their perimeter may be compromised by attackers
through software supply chain, privileged user compromise or other
attacks. Workloads compromised through external attacks, malicious
insiders or software errors can cause any or all of the following
unauthorized actions:
* Invocations of workloads in the network without any external
invocation being present
* Arbitrary user impersonation
* Parameter modification or augmentation
The results of these actions are unauthorised access to resources.
2. Overview
Transaction Tokens (Txn-Token) are a means to mitigate damage from
such attacks or spurious invocations. A valid Txn-Token indicates a
valid external invocation. They ensure that the identity of the user
or a workload that made the external request is preserved throughout
subsequent workload invocations. They preserve any context such as:
* Parameters of the original call
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* Environmental factors, such as IP address of the original caller
* Any computed context that needs to be preserved in the call chain.
This includes information that was not in the original request to
the external endpoint.
Cryptographically protected Txn-Tokens ensure that downstream
workloads cannot make unauthorized modifications to such information,
and cannot make spurious calls without the presence of an external
trigger.
2.1. What are Transaction Tokens?
Txn-Tokens are short-lived, signed JWTs [RFC7519] that assert the
identity of a user or a workload and assert an authorization context.
The authorization context provides information expected to remain
constant during the execution of a call as it passes through multiple
workloads.
2.2. Creating Txn-Tokens
2.2.1. Initial Creation
Txn-Tokens are typically created when a workload is invoked using an
endpoint that is externally visible, and is authorized using a
separate mechanism, such as an OAuth [RFC6749] access token or an
OpenID Connect [OpenIdConnect] ID token. This workload then performs
an OAuth 2.0 Token Exchange [RFC8693] to obtain a Txn-Token. To do
this, it invokes a special Token Service (the Txn-Token Service) and
provides context that is sufficient for it to generate a Txn-Token.
This context MAY include:
* The external authorization token (e.g., the OAuth access token)
* Parameters that are required to be bound for the duration of this
call
* Additional context, such as the incoming IP address, User Agent
information, or other context that can help the Txn-Token Service
to issue the Txn-Token
The Txn-Token Service responds to a successful invocation by
generating a Txn-Token. The calling workload then uses the Txn-Token
to authorize its calls to subsequent workloads. Subsequent workloads
may obtain Txn-Tokens of their own.
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2.2.2. Replacement Txn-Tokens
A service within a call chain may choose to replace the Txn-Token.
This can typically happen if the service wants to add to the context
of the current Txn-Token
To get a replacement Txn-Token, a service will request a new Txn-
Token from the Txn-Token Service and provide the current Txn-Token
and other parameters in the request. The Txn-Token service must
exercise caution in what kinds of replacement requests it supports so
as to not negate the entire value of Txn-Tokens.
2.3. Txn-Token Lifetime
Txn-Tokens are expected to be short-lived (order of minutes, e.g., 5
minutes), and as a result MAY be used only for the expected duration
of an external invocation. If the token or other credential
presented to the Txn-Token service when requesting a Txn-Token has an
expiration time, then the Txn-Token MUST NOT exceed the lifetime of
the originally presented token or credential. If a long-running
process such as an batch or offline task is involved, it can use a
separate mechanism to perform the external invocation, but the
resulting Txn-Token is still short-lived.
2.4. Benefits of Txn-Tokens
Txn-Tokens help prevent spurious invocations by ensuring that a
workload receiving an invocation can independently verify the user or
workload on whose behalf an external call was made and any context
relevant to the processing of the call. Through the presence of
additional signatures on the Txn-Token, a workload receiving an
invocation can also independently verify that specific workloads were
within the path of the call before it was invoked.
2.5. Txn-Token Issuance and Usage Flows
2.5.1. Basic Flow
Figure 1 shows the basic flow of how Txn-Tokens are used in an a
multi-workload environment.
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1 ┌──────────────┐ 2 ┌──────────────┐
─────────▶│ ├───────────▶ │
│ External │ │ Txn-Token │
7 │ Endpoint │ 3 │ Service │
◀─────────┤ ◀───────────│ │
└────┬───▲─────┘ └──────────────┘
│ │
4 │ │ 6
┌────▼───┴─────┐
│ │
│ Internal │
│ µ-service │
│ │
└────┬───▲─────┘
│ │
▼ │
o
5 o 6
o
│ ▲
│ │
┌────▼───┴─────┐
│ │
│ Internal │
│ µ-service │
│ │
└──────────────┘
Figure 1: Basic Transaction Tokens Architecture
1. External endpoint is invoked using conventional authorization
mechanism such as an OAuth 2.0 Access token
2. External endpoint provides context and incoming authorization
(e.g., access token) to the Txn-Token Service
3. Txn-Token Service mints a Txn-Token that provides immutable
context for the transaction and returns it to the requester
4. The external endpoint initiates a call to an internal
microservice and provides the Txn-Token as authorization
5. Subsequent calls to other internal microservices use the same
Txn-Token to authorize calls
6. Responses are provided to callers based on successful
authorization by the invoked microservices
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7. External client is provided a response to the external invocation
2.5.2. Replacement Txn-Token Flow
An intermediate service may decide to obtain a replacement Txn-Token
from the Txn-Token service. That flow is described below in Figure 2
1 ┌──────────────┐ 2 ┌──────────────┐
─────────▶│ ├───────────▶ │
│ External │ │ │
10 │ Endpoint │ 3 │ │
◀─────────┤ ◀───────────│ │
└────┬───▲─────┘ │ │
│ │ │ │
4 │ │ 9 │ │
┌────▼───┴─────┐ │ │
│ │ │ │
│ Internal │ │ │
│ µ-service │ │ │
│ │ │ │
└────┬───▲─────┘ │ Txn-Token │
│ │ │ Service │
▼ │ │ │
o │ │
5 o 9 │ │
│ o ▲ │ │
│ │ │ │
│ │ │ │
┌────▼───┴─────┐ 6 │ │
│ ├───────────▶ │
│ Internal │ │ │
│ µ-service │ 7 │ │
│ ◀───────────│ │
└────┬───▲─────┘ │ │
│ │ │ │
▼ │ └──────────────┘
o
8 o 9
o
│ ▲
│ │
┌────▼───┴─────┐
│ │
│ Internal │
│ µ-service │
│ │
└──────────────┘
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Figure 2: Replacement Txn-Token Flow
In the diagram above, steps 1-5 are the same as in Section 2.5.1
6. An intermediate service determines that it needs to obtain a
Replacement Txn-Token. It requests a Replacement Txn-Token from
the Txn-Token Service. It passes the incoming Txn-Token in the
request, along with any additional context it needs to send the
Txn-Token Service.
7. The Txn-Token Service responds with a replacement Txn-Token
8. The service that requested the Replacement Txn-Token uses that
Txn-Token for downstream call authorization
9. Responses are provided to callers based on successful
authorization by the invoked microservices
10. External client is provided a response to the external invocation
3. Notational Conventions
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.
4. Terminology
Workload: An independent computational unit that can autonomously
receive and process invocations, and can generate invocations of
other workloads. Examples of workloads include containerized
microservices, monolithic services and infrastructure services
such as managed databases.
Trust Domain: A virtually or physically separated network, which
contains two or more workloads. The workloads within an Trust
Domain may be invoked only through published interfaces. A Trust
Domain must have an identifier that is used as the aud (audience)
value in Txn-Tokens. The format of this identifier is as defined
in the JWT specification [RFC7519].
External Endpoint: A published interface to an Trust Domain that
results in the invocation of a workload within the Trust Domain.
Call Chain: A sequence of invocations that results from the
invocation of an external endpoint.
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Transaction Token (Txn-Token): A signed JWT that has a short
lifetime, which provides immutable information about the user or
workload, certain parameters of the call and certain contextual
attributes of the call.
Authorization Context: A JSON object containing a set of claims that
represent the immutable context of a call chain.
Transaction Token Service (Txn-Token Service): A special service
within the Trust Domain, which issues Txn-Tokens to requesting
workloads. Each Trust Domain has exactly one Txn-Token Service.
5. Txn-Token Format
A Txn-Token is a JSON Web Token [RFC7519] protected by a JSON Web
Signature [RFC7515]. The following describes the required values in
a Txn-Token:
5.1. JWT Header
In the JWT Header:
* The typ claim MUST be present and MUST have the value txn_token.
* Key rotation of the signing key SHOULD be supported through the
use of a kid claim.
Figure 3 is a non-normative example of the JWT Header of a Txn-Token
{
"typ": "txn_token",
"alg": "RS256",
"kid": "identifier-to-key"
}
Figure 3: Example: Txn-Token Header
5.2. JWT Body Claims
The transaction token body follows the JWT format and includes
existing JWT claims as well as defines new claims. These claims are
described below:
iss: OPTIONAL The iss claim as defined in [RFC7519] is not required
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as Txn-Tokens are bound to a single trust domain as defined by the
aud claim and often the signing keys are known. The iss claim
MUST be used in cases where the signing keys are not predetermined
or it is desired that the Txn-Token Service signs with unique
keys.
iat: REQUIRED The issued at time of the Txn-Token as defined in
[RFC7519]
aud: REQUIRED This claim, defined in [RFC7519], contains the trust
domain in which the Txn-Token is valid
exp: REQUIRED Expiry time of the Txn-Token as defined in [RFC7519]
txn: REQUIRED A unique transaction identifier as defined in
Section 2.2 of [RFC8417]. When used in the transaction token, it
identifies the entire call chain.
sub: REQUIRED A unique identifier for the subject as defined by the
aud trust domain. Unlike OpenID Connect, the sub claim is NOT
associated with the iss claim.
purp: REQUIRED A String defining the purpose or intent of this
transaction.
azd: OPTIONAL A JSON object that conatains values that remain
immutable throughout the call chain.
rctx: OPTIONAL A JSON object that describes the environmental
context of the requested transaction.
5.2.1. Requester Context
The Txn-Token SHOULD contain an rctx claim. This MAY include the IP
address information of the originating user, as well as information
about the computational entity that requested the Txn-Token and
contextual attributes of the originating request itself.
The JSON value of the rctx claim MAY include any values the Txn-Token
Service determines are interesting to downstream services that rely
on the Txn-Token. The following claims are defined so that if they
are included, they have the following meaning:
* req_ip The IP address of the requester. This MAY be the end-user
or a robotic process that requested the Transaction
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* authn The authentication method used to idenitfy the requester.
Its value is a StringOrURI that uniquely identifies the method
used.
* req_wl The requesting workload. A StringOrURI that uniquely
identifies the computational entity that requested the Txn-Token.
This entity MUST be within the Trust Domain of the Txn-Token. If
a replacement Txn-Token has been requested, then this claim will
be an array of StringOrURIs representing the different workloads
that have requested Txn-Tokens as part of the transaction
processing.
5.2.1.1. Requesting Workload Identifier
It is useful to be able to track the set of workloads that have
requested a Txn-Token. The req_wl claim allows for tracking this
information even through requests for a replacement Txn-Token. By
default the req_wl is a StringOrURI representing the original
workload entity that requested the Txn-Token. However, if a workload
within the path of servicing the transaction requests a replacement
Txn-Token, then the Transaction Token Service will append the new
requesting workload as a subsequent array element in the req_wl
claim. This provides a "pathing" mechanism to track which services
have requested replacement Txn-Tokens. If there is only a single
value the req_wl will be a StringOrURI. If there is more than a
single value, then req_wl will be prepresented by an array of
StringOrURIs.
{
"rctx": {
"req_ip": "69.151.72.123", // env context of external call
"authn": "urn:ietf:rfc:6749", // env context of the external call
"req_wl": [ "apigateway.trust-domain.example", "workload3.trust-domain.example" ]
}
5.2.2. Example
The figure below Figure 4 shows a non-normative example of the JWT
body of a Txn-Token:
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{
"iat": "1686536226000",
"aud": "trust-domain.example",
"exp": "1686536526000",
"txn": "97053963-771d-49cc-a4e3-20aad399c312",
"sub": "d084sdrt234fsaw34tr23t",
"rctx": {
"req_ip": "69.151.72.123", // env context of external call
"authn": "urn:ietf:rfc:6749", // env context of the external call
"req_wl": "apigateway.trust-domain.example" // the internal entity that requested the Txn-Token
},
"purp" : "trade.stocks",
"azd": {
"action": "BUY", // parameter of external call
"ticker": "MSFT", // parameter of external call
"quantity": "100", // parameter of external call
"user_level": "vip" // computed value not present in external call
}
}
Figure 4: Example: Txn-Token Body
6. Txn-Token Service
A Txn-Token Service defines a profile of the OAuth 2.0 Token Exchange
[RFC8693] endpoint that can respond to Txn-Token issuance requests.
This profile of the OAuth 2.0 Token Exchange [RFC8693] specification
MUST be used to obtain Txn-Tokens. The unique properties of the Txn-
Token requests and responses are described below. The Txn-Token
Service MAY optionally support other OAuth 2.0 endpoints and
features, but that is not a requirement for it to be a Txn-Token
Service.
Each Trust Domain MUST have exactly one logical Txn-Token Service.
7. Requesting Txn-Tokens
A workload requests a Txn-Token from a Transaction Token Service
using a profile of the OAuth 2.0 Token Exchange [RFC8693]. Txn-
Tokens may be requested for both externally originating or internally
originating requests. The profile describes how required and
optional context can be provided to the Transaction Token Service in
order for the Txn-Token to be issued. The request to obtain a Txn-
Token using this method is called a Txn-Token Request, and a
successful response is called a Txn-Token Response. The Txn-Token
profile of the OAuth 2.0 Token Exchange [RFC8693] is described below.
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7.1. Txn-Token Request
A workload requesting a Txn-Token must provide the Transaction Token
Service with proof of its identity (client authentication), the
purpose of the Txn-Token and optionally any additional context
relating to the transaction being performed. Most of these elements
are provided by the OAuth 2.0 Token Exchange specification and the
rest are defined as new parameters. Additionally, this profile
defines a new token type URN urn:ieft:params:oauth:token-type:txn-
token which is used by the requesting workload to identify that it is
requesting the Txn-Token Response to contain a Txn-Token.
To request a Txn-Token the workload invokes the OAuth 2.0 [RFC6749]
token endpoint with the following parameters: * grant_type REQUIRED.
The value MUST be set to urn:ietf:params:oauth:grant-type:token-
exchange * audience REQUIRED. The value MUST be set to the Trust
Domain name * scope REQUIRED. A space-delimited list of case-
sensitive strings where the value(s) MUST represent the specific
purpose or intent of the transaction. * requested_token_type
REQUIRED. The value MUST be urn:ietf:params:oauth:token-type:txn-
token * subject_token REQUIRED. The value MUST represent the subject
of the transaction. This could be an OAuth access_token received by
an API Gateway, a JWT assertion constructed by a workload initiating
a transaction or a simple string value all identified by
subject_token_type. * subject_token_type REQUIRED. The value MUST
indicate the type of the token or value present in the subject_token
parameter
The following additional parameters MAY be present in a Txn-Token
Request:
* request_context OPTIONAL. This parameter contains a base64url
encoded JSON object which represents the context of this
transaction. The parameter SHOULD be present and how the
Transaction Token Service uses this parameter is out of scope for
this specification.
* request_details OPTIONAL. This parameter contains a base64url
encoded JSON object which represents additional details of the
transaction that MUST remain immutable throughout the processing
of the transaction by multiple workloads.
The requesting workload MUST authenticate its identity to the
Transaction Token Service. The exact client authentication mechanism
used is outside the scope of this specification.
Figure 5 shows a non-normative example of a Txn-Token Request.
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POST /txn-token-service/token_endpoint HTTP 1.1
Host: txn-token-service.trust-domain.example
Content-Type: application/x-www-form-urlencoded
grant_type=urn%3Aietf%3Aparams%3Aoauth%3Agrant-type%3Atoken-exchange
&requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Atxn-token
&audience=http%3A%2F%2Ftrust-domain.example
&scope=finance.watchlist.add
&subject_token=eyJhbGciOiJFUzI1NiIsImtpZC...kdXjwhw
&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token
&request_context=eyAiaXBfYWRkcmVzcyI6ICIxMjcuMC4wLjEiLCAiY2xpZW50IjogIm1vYmlsZS1hcHAiLCAiY2xpZW50X3ZlcnNpb24iOiAidjExIiB9
Figure 5: Example: Txn-Token Request
7.2. Txn-Token Request Processing
When the Transaction Token Service receives a Txn-Token Request it
MUST validate the requesting workload client authentication and
determine if that workload is authorized to obtain the Txn-Tokens
with the requested values. The authorization policy for determining
such issuance is out of scope for this specification.
Next, the Transaction Token Service MUST validate the subject_token
and determine the value to specify as the sub of the issued Txn-
Token. The Txn-Token Service MUST ensure the sub value is unique
within the trust domain defined by the aud claim.
The Transaction Token Service MUST set the iat claim to the time of
issuance of the Txn-Token. The Transaction Token Service MUST set
the aud claim to a Trust Domain of the Transaction Token Service. If
the Transaction Token Service supports multiple trust domains, then
it MUST determine the correct aud value for this request. The
Transaction Token Service MUST set the exp claim to the expiry time
of the Txn-Token. The Transaction Token Service MUST set the txn
claim to a unique ID specific to this transaction.
The Transaction Token Service MAY set the iss claim of the Txn-Token
to a value defining the entity that signed the Txn-Token. This claim
MUST be ommitted if not set.
The Transaction Token Service MUST evaluate the value specified in
the scope parameter of the request to determine the purp claim of the
issued Txn-Token.
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If a request_context parameter is present in the Txn-Token Request,
the data SHOULD be added to the rctx object of the Txn-Token. In
addition, the Transaction Token Service SHOULD add the authenticated
requesting workload identifier in the rctx object as the req_wl
claim.
If a request_details parameter is present in the Txn-Token Request,
then the Transaction Token Service SHOULD propagate the data from the
request_details object into the claims in the azd object as
authorized by the Transaction Token Service authorization policy for
the requesting client.
The Transaction Token Service MAY provide additional processing and
verification that is outside the scope of this specification.
7.3. Txn-Token Response
A successful response to a Txn-Token Request by a Transaction Token
Service is called a Txn-Token Response. If the Transaction Token
Service responds with an error, the error response is as described in
Section 5.2 of [RFC6749]. The following describes required values of
a Txn-Token Response:
* The token_type value MUST be set to N_A per guidance in OAuth 2.0
Token Exchange [RFC8693]
* The access_token value MUST be the Txn-Token JWT
* The issued_token_type value MUST bet set to
urn:ieft:params:oauth:token-type:txn-token
* The response MUST NOT include the values expires_in, refresh_token
and scope
Figure 6 shows a non-normative example of a Txn-Token Response.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache, no-store
{
"token_type": "N_A",
"issued_token_type": "urn:ieft:params:oauth:token-type:txn-token",
"access_token": "eyJCI6IjllciJ9...Qedw6rx"
}
Figure 6: Example: Txn-Token Response
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7.4. Creating Replacement Txn-Tokens
A workload within a call chain may request the Transaction Token
Server to replace a Txn-Token.
Workloads MAY request replacement Txn-Tokens in order to change (add
to, remove or modify) the asserted values within a Txn-Token.
The values of the sub and aud claims MUST remain unchanged in a
replacement Txn-Token. If the claim rctx is present in the original
Txn-Token, then it MUST be present and unchanged in the replacement
Txn-Token except for the req_wl claim which MUST be updated to
include the requesting workload identifier.
7.4.1. Txn-Token Service Responsibilities
A Txn-Token Service replacing a Txn-Token must consider that
modifying previously asserted values from existing Txn-Tokens can
completely negate the benefits of Txn-Tokens. When issuing
replacement Txn-Tokens, a Transaction Token Server therefore:
* MAY enable modifications to asserted values that reduce the scope
of permitted actions
* MAY enable additional asserted values
* SHOULD NOT enable modification to asserted values that expand the
scope of permitted actions
7.4.2. Replacement Txn-Token Request
To request a replacement Txn-Token, the requester makes a Txn-Token
Request as described in Section 7.1 but includes the Txn-Token to be
replaced as the value of the subject_token parameter.
7.4.3. Replacement Txn-Token Response
A successful response by the Transaction Token Server to a
Replacement Txn-Token Request is a Txn-Token Response as described in
Section 7.3
7.5. Mutual Authentication of the Txn-Token Request
A Txn-Token Service MUST ensure that it authenticates any workloads
requesting Txn-Tokens. In order to do so:
* It MUST name a limited, pre-configured set of workloads that MAY
request Txn-Tokens
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* It MUST individually authenticate the requester as being one of
the named requesters
* It SHOULD rely on mechanisms, such as [Spiffe] or some other means
of performing MTLS [RFC8446], to securely authenticate the
requester
* It SHOULD NOT rely on insecure mechanisms, such as long-lived
shared secrets to authenticate the requesters
The requesting workload MUST have a pre-configured location for the
Transaction Token Service. It SHOULD rely on mechanisms, such as
[Spiffe], to securely authenticate the Transaction Token Service
before making a Txn-Token Request.
8. Using Txn-Tokens
Txn-Tokens need to be communicated between workloads that depend upon
them to authorize the request. Such workloads will often present
HTTP [RFC9110] interfaces for being invoked by other workloads. This
section specifies the HTTP header the invoking workload MUST use to
communicate the Txn-Token to the invoked workload, when the invoked
workload presents an HTTP interface. Note that the standard HTTP
Authorization header MUST NOT be used because that may be used by the
workloads to communicate channel authorization.
8.1. Txn-Token HTTP Header
A workload that invokes another workload using HTTP and needs to
present a Txn-Token to the invoked workload MUST use the HTTP Header
Txn-Token to communicate the Txn-Token. The value of this header
MUST be the JWT that represents the Txn-Token.
9. Security Considerations
9.1. Txn-Token Lifetime
A Txn-Token is not resistant to replay attacks. A long-lived Txn-
Token therefore represents a risk if it is stored in a file,
discovered by an attacker, and then replayed. For this reason, a
Txn-Token lifetime must be kept short, not exceeding the lifetime of
a call-chain. Even for long-running "batch" jobs, a longer lived
access token should be used to initiate the request to the batch
endpoint. It then obtains short-lived Txn-Tokens that may be used to
authorize the call to downstream services in the call-chain.
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Because Txn-Tokens are short-lived, the Txn-Token response from the
Txn-Token service does not contain the refresh_token field. A Txn-
Token cannot be issued by presenting a refresh_token.
The expires_in and scope fields of the OAuth 2.0 Token Exchange
specification [RFC8693] are also not used in Txn-Token responses.
The expires_in is not required since the issued token has an exp
field, which indicates the token lifetime. The scope field is
omitted from the request and therefore omitted in the response.
9.2. Access Tokens
When creating Txn-Tokens, the Txn-Token MUST NOT contain the Access
Token presented to the external endpoint. If an Access Token is
included in a Txn-Token, an attacker may extract the Access Token
from the Txn-Token, and replay it to any Resource Server that can
accept that Access Token. Txn-Token expiry does not protect against
this attack since the Access Token may remain valid even after the
Txn-Token has expired.
9.3. Client Authentication
How requesting clients authenticate to the Transaction Token Service
is out of scope for this specification. However, if using the
actor_token and actor_token_type parameters of the OAuth 2.0 Token
Exchange specification, both parameters MUST be present in the
request. The actor_token MUST autenticate the identity of the
requesting workload.
10. Privacy Considerations
10.1. Obsfucation of Personal Information
Some rctx claims may be considered personal information in some
jurisdictions and if so their values need to be obsfucated. For
example, originating IP address (req_ip) is often considerd personal
information and in that case must be protected through some
obsfucation method (e.g. SHA256).
11. IANA Considerations
This specification registers the following claims defined in
Section Section 5.1 to the OAuth Access Token Types Registry defined
in [RFC6749], and the following claims defined in Section Section 5.2
in the IANA JSON Web Token Claims Registry defined in [RFC7519]
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11.1. OAuth Registry Contents
* Name: txn_token
* Description: JWT of type Transaction Token
* Additional Token Endpoint Response Parameters: none
* HTTP Authentication Schemes: TLS [RFC8446]
* Change Controller: IESG
* Specification Document: Section Section 5.1 of this specificaiton
11.2. JWT Registry Contents
* Claim Name: azd
- Claim Description: The authorization context details
- Change Controller: IESG
- Specification Document: Section Section 5.2 of this
specification
* Claim Name: rctx
- Claim Description: The requester context
- Change Controller: IESG
- Specification Document: Section Section 5.2.1 of this
specification
* Claim Name: purp
- Claim Description: The purpose of the transaction
- Change Controller: IESG
- Specification Document: Section Section 5.2 of this
specification
12. References
12.1. Normative References
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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,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[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/rfc/rfc7519>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/rfc/rfc7515>.
[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/rfc/rfc8174>.
[RFC8693] Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J.,
and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693,
DOI 10.17487/RFC8693, January 2020,
<https://www.rfc-editor.org/rfc/rfc8693>.
[RFC8417] Hunt, P., Ed., Jones, M., Denniss, W., and M. Ansari,
"Security Event Token (SET)", RFC 8417,
DOI 10.17487/RFC8417, July 2018,
<https://www.rfc-editor.org/rfc/rfc8417>.
[RFC9110] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP Semantics", STD 97, RFC 9110,
DOI 10.17487/RFC9110, June 2022,
<https://www.rfc-editor.org/rfc/rfc9110>.
[OpenIdConnect]
Sakimura, N., Bradley, J., Jones, M., Medeiros, B. de.,
and C. Mortimore, "OpenID Connect Core 1.0 incorporating
errata set 1", November 2014,
<https://openid.net/specs/openid-connect-core-1_0.html>.
12.2. Informative References
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[Spiffe] Cloud Native Computing Foundation, "Secure Production
Identity Framework for Everyone", n.d.,
<https://spiffe.io/docs/latest/spiffe-about/overview/>.
Acknowledgements
Contributors
Dr. Kelley W. Burgin, PhD.
MITRE Corporation
Email: kburgin@mitre.org
Brian Campbell
Ping Identity
Email: bcampbell@pingidentity.com
Evan Gilman
SPIRL
Email: evan@spirl.com
Kai Lehmann
1&1 Mail & Media Development & Technology GmbH
Email: kai.lehmann@1und1.de
Arndt Schwenkschuster
Microsoft
Email: arndts@microsoft.com
Hannes Tschofenig
Arm Ltd.
Email: Hannes.Tschofenig@arm.com
Authors' Addresses
Atul Tulshibagwale
SGNL
Email: atul@sgnl.ai
George Fletcher
Capital One
Email: george.fletcher@capitalone.com
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Pieter Kasselman
Microsoft
Email: pieter.kasselman@microsoft.com
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