Internet DRAFT - draft-oauth-transaction-tokens
draft-oauth-transaction-tokens
oauth A. Tulshibagwale
Internet-Draft SGNL
Intended status: Informational G. Fletcher
Expires: 31 May 2024 Capital One
P. Kasselman
Microsoft
28 November 2023
Transaction Tokens
draft-oauth-transaction-tokens-00
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.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 31 May 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
Tulshibagwale, et al. Expires 31 May 2024 [Page 1]
Internet-Draft Txn-Tokens November 2023
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
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 . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2.1. Required Claims . . . . . . . . . . . . . . . . . . . 9
5.2.2. Optional Claims . . . . . . . . . . . . . . . . . . . 10
5.2.3. Example . . . . . . . . . . . . . . . . . . . . . . . 11
6. Txn-Token Service . . . . . . . . . . . . . . . . . . . . . . 11
7. Requesting Txn-Tokens . . . . . . . . . . . . . . . . . . . . 12
7.1. Txn-Token Request . . . . . . . . . . . . . . . . . . . . 12
7.2. Txn-Token Response . . . . . . . . . . . . . . . . . . . 13
7.3. Creating Replacement Txn-Tokens . . . . . . . . . . . . . 13
7.3.1. Txn-Token Service Responsibilities . . . . . . . . . 14
7.3.2. Replacement Txn-Token Request . . . . . . . . . . . . 14
7.3.3. Replacement Txn-Token Response . . . . . . . . . . . 14
7.4. Mutual Authentication of the Txn-Token Request . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8.1. Txn-Token Lifetime . . . . . . . . . . . . . . . . . . . 15
8.2. Sender Constrained Tokens . . . . . . . . . . . . . . . . 15
8.3. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 15
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 16
9.1. Obsfucation of Personal Information . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
10.1. OAuth Registry Contents . . . . . . . . . . . . . . . . 16
10.2. JWT Registry Contents . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 18
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 18
Tulshibagwale, et al. Expires 31 May 2024 [Page 2]
Internet-Draft Txn-Tokens November 2023
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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
* 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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 3]
Internet-Draft Txn-Tokens November 2023
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.
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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 4]
Internet-Draft Txn-Tokens November 2023
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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 5]
Internet-Draft Txn-Tokens November 2023
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
Tulshibagwale, et al. Expires 31 May 2024 [Page 6]
Internet-Draft Txn-Tokens November 2023
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 │
│ │
└──────────────┘
Tulshibagwale, et al. Expires 31 May 2024 [Page 7]
Internet-Draft Txn-Tokens November 2023
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 a universal
resource identifier. Each Trust Domain has exactly one Txn-Token
Service.
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
Tulshibagwale, et al. Expires 31 May 2024 [Page 8]
Internet-Draft Txn-Tokens November 2023
invocation of an external endpoint.
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
5.2.1. Required Claims
The JWT body MUST have the following claims:
* An iss claim, whose value is a URN [RFC8141] that uniquely
identifies the workload or the Txn-Token Service that created the
Txn-Token.
Tulshibagwale, et al. Expires 31 May 2024 [Page 9]
Internet-Draft Txn-Tokens November 2023
* An iat claim, whose value is the time at which the Txn-Token was
created.
* An aud claim, whose value is a URN [RFC8141] that uniquely
identifies the audience of the Txn-Token. This MUST identify the
trust domain in which the Txn-Token is used.
* An exp claim, whose value is the time at which the Txn-Token
expires.
* A txn claim, whose value is the unique transaction identifier as
defined in Section 2.2 of [RFC8417]. When used in the transaction
token, it identifies the entire call chain.
* A sub_id claim, whose value is the unique identifier of the user
or workload on whose behalf the call chain is being executed. The
format of this claim MAY be a Subject Identifier as specified in
[SubjectIdentifiers].
* An azd claim, whose value is a JSON object that contains values
that remain constant in the call chain.
5.2.2. Optional Claims
The JWT body MAY have the following claims:
5.2.2.1. Requester Context
The Txn-Token MAY contain an req_ctx claim, whose value is a JSON
object the describes the requester context of the transaction. This
MAY include the IP address information of the originating user, as
well as information about the computational entity that requested the
Txn-Token.
The JSON value of the req_ctx 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
* authn The authentication method used to idenitfy the requester.
Its value is a URN that uniquely identifies the method used.
* req_wl The requesting workload. A URN that uniquely identifies
the computational entity that requested the Txn-Token. This
entity MUST be within the Trust Domain of the Txn-Token.
Tulshibagwale, et al. Expires 31 May 2024 [Page 10]
Internet-Draft Txn-Tokens November 2023
5.2.2.2. Purpose
The Txn-Token MAY contain a purp claim, whose value specifies the
purpose of the transaction. The format of this claim is a JSON
string.
5.2.3. Example
The figure below Figure 4 shows a non-normative example of the JWT
body of a Txn-Token:
{
"iss": "https://trust-domain.example/txn-token-service",
"iat": "1686536226000",
"aud": "trust-domain.example",
"exp": "1686536526000",
"txn": "97053963-771d-49cc-a4e3-20aad399c312",
"sub_id": {
"format": "email",
"email": "user@trust-domain.example"
},
"req_ctx": {
"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 provides a OAuth 2.0 Token Exchange [RFC8693]
endpoint that can respond to Txn-Token issuance requests. The token
exchange requests it supports require extra parameters than those
defined in the OAuth 2.0 Token Exchange [RFC8693] specification. 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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 11]
Internet-Draft Txn-Tokens November 2023
Each Trust Domain MUST have exactly one Txn-Token Service.
7. Requesting Txn-Tokens
A workload requests a Txn-Token from a Transaction Token Service
using OAuth 2.0 Token Exchange [RFC8693]. 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. A Txn-Token
Request is a Token Exchange Request, as described in Section 2.1 of
[RFC8693] with additional parameters. A Txn-Token Response is a
OAuth 2.0 token endpoint response, as described in Section 5 of
[RFC6749], where the token_type in the response has the value
txn_token.
7.1. Txn-Token Request
A Txn-Token Request is an OAuth 2.0 Token Exchange Request, as
described in Section 2.1 of [RFC8693], with an additional parameter
in the request. The following parameters are required in the Txn-
Token Request by the OAuth 2.0 Token Exchange specification
[RFC8693]:
* The audience value MUST be set to the Trust Domain name
* The requested_token_type value MUST be
urn:ietf:params:oauth:token-type:txn_token
* The subject_token value MUST be the external token received by the
workload that authorized the call
* The subject_token_type value MUST be present and indicate the type
of the authorization token present in the subject_token parameter
The following additional parameter MUST be present in a Txn-Token
Request:
* A parameter named rctx , whose value is a JSON object. This
object contains the request context, i.e. any information the
Transaction Token Service needs to understand the context of the
incoming request
Figure 5 shows a non-normative example of a Txn-Token Request.
Tulshibagwale, et al. Expires 31 May 2024 [Page 12]
Internet-Draft Txn-Tokens November 2023
POST /txn-token-service/token_endpoint HTTP 1.1
Host: txn-token-service.trust-domain.example
Content-Type: application/x-www-form-urlencoded
requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Atxn_token
&audience=http%3A%2F%2Ftrust-domain.example
&subject_token=eyJhbGciOiJFUzI1NiIsImtpZC...kdXjwhw
&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token
&rctx=%7B%22param1%22%3A%22value1%22%2C%22param2%22%3A%22value2%22%2C%22ip_address%22%3A%2269.151.72.123%22%7D
Figure 5: Example: Txn-Token Request
7.2. 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 txn_token
* The access_token value MUST be the 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
{
"issued_token_type": "urn:ietf:params:oauth:token-type:txn_token",
"access_token": "eyJCI6IjllciJ9...Qedw6rx"
}
Figure 6: Example: Txn-Token Response
7.3. 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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 13]
Internet-Draft Txn-Tokens November 2023
The value of the aud claim MUST remain unchanged in a replacement
Txn-Token. If the claim req_ctx is present in the original Txn-
Token, then it MUST be present unchanged in the replacement Txn-
Token.
7.3.1. 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
7.3.2. 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.
7.3.3. 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 7.2
7.4. 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
* 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
Tulshibagwale, et al. Expires 31 May 2024 [Page 14]
Internet-Draft Txn-Tokens November 2023
* 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. Security Considerations
8.1. 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.
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.
8.2. Sender Constrained Tokens
Although Txn-Tokens are short-lived, they MAY be sender constrained
as an additional layer of defence to prevent them from being re-used
by a compromised or malicious workload under the control of a hostile
actor.
8.3. 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.
Tulshibagwale, et al. Expires 31 May 2024 [Page 15]
Internet-Draft Txn-Tokens November 2023
9. Privacy Considerations
9.1. Obsfucation of Personal Information
Some req_ctx 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).
10. 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 5.2.1 in the IANA JSON Web Token Claims Registry
defined in [RFC7519]
10.1. 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
10.2. JWT Registry Contents
* Claim Name: azd
- Claim Description: The authorization context details
- Change Controller: IESG
- Specification Document: Section Section 5.2.1 of this
specification
* Claim Name: req_ctx
- Claim Description: The requester context
- Change Controller: IESG
Tulshibagwale, et al. Expires 31 May 2024 [Page 16]
Internet-Draft Txn-Tokens November 2023
- Specification Document: Section Section 5.2.2.1 of this
specification
* Claim Name: purp
- Claim Description: The purpose of the transaction
- Change Controller: IESG
- Specification Document: Section Section 5.2.2.2 of this
specification
11. References
11.1. Normative References
[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>.
[RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
(URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
<https://www.rfc-editor.org/rfc/rfc8141>.
[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>.
Tulshibagwale, et al. Expires 31 May 2024 [Page 17]
Internet-Draft Txn-Tokens November 2023
[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>.
[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>.
[SubjectIdentifiers]
Backman, A., Scurtescu, M., and P. Jain, "Subject
Identifiers for Security Event Tokens", n.d.,
<https://datatracker.ietf.org/doc/html/draft-ietf-
secevent-subject-identifiers>.
11.2. Informative References
[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
Hannes Tschofenig
Arm Ltd.
Email: Hannes.Tschofenig@arm.com
Evan Gilman
SPIRL
Email: evan@spirl.com
Tulshibagwale, et al. Expires 31 May 2024 [Page 18]
Internet-Draft Txn-Tokens November 2023
Arndt Schwenkschuster
Microsoft
Email: arndts@microsoft.com
Authors' Addresses
Atul Tulshibagwale
SGNL
Email: atul@sgnl.ai
George Fletcher
Capital One
Email: george.fletcher@capitalone.com
Pieter Kasselman
Microsoft
Email: pieter.kasselman@microsoft.com
Tulshibagwale, et al. Expires 31 May 2024 [Page 19]
