oauth A. Tulshibagwale
Internet-Draft SGNL
Intended status: Informational G. Fletcher
Expires: 8 January 2024 Capital One
P. Kasselman
Microsoft
7 July 2023
Transaction Tokens
draft-tulshibagwale-oauth-transaction-tokens-00
Abstract
Transaction Tokens (Tx-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, is preserved and
available to all workloads that are invoked as part of processing
such a request. Tx-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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. What are Transaction Tokens? . . . . . . . . . . . . . . 3
2.2. Creating Tx-Tokens . . . . . . . . . . . . . . . . . . . 4
2.2.1. Leaf Tx-Tokens . . . . . . . . . . . . . . . . . . . 4
2.2.2. Nested Tx-Tokens . . . . . . . . . . . . . . . . . . 4
2.3. Tx-Token Lifetime . . . . . . . . . . . . . . . . . . . . 4
2.4. Benefits of Tx-Tokens . . . . . . . . . . . . . . . . . . 5
2.5. Tx-Token Issuance and Usage Flows . . . . . . . . . . . . 5
3. Notational Conventions . . . . . . . . . . . . . . . . . . . 7
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Tx-Token Format . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. JWT Header . . . . . . . . . . . . . . . . . . . . . . . 8
5.2. JWT Body . . . . . . . . . . . . . . . . . . . . . . . . 9
5.2.1. Common Claims . . . . . . . . . . . . . . . . . . . . 9
5.2.2. Leaf Tx-Token Claims . . . . . . . . . . . . . . . . 9
5.2.3. Nested Tx-Token Claim . . . . . . . . . . . . . . . . 10
6. Requesting Leaf Tx-Tokens . . . . . . . . . . . . . . . . . . 11
6.1. Tx-Token Request . . . . . . . . . . . . . . . . . . . . 11
6.2. Tx-Token Response . . . . . . . . . . . . . . . . . . . . 12
7. Creating Nested Tx-Tokens . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9.1. Mutual Authentication of the Tx-Token Request . . . . . . 13
9.2. Sender Constrained Tokens . . . . . . . . . . . . . . . . 13
9.3. Access Tokens . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 15
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 15
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
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
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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 (Tx-Token) are a means to mitigate damage from
such attacks or spurious invocations. A valid Tx-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 Tx-Token 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?
Tx-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.
When necessary, a Tx-Token may include embedded tokens, as described
in [JWTEmbeddedTokens]. This is called Nested Tx-Token. This
nesting enables workloads in a call chain to assert their invocation
during the call chain to downstream workloads.
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2.2. Creating Tx-Tokens
2.2.1. Leaf Tx-Tokens
Tx-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] token or an OpenID
Connect [OpenIdConnect] token. We call this token "Leaf Tx-Token".
This workload then performs an OAuth 2.0 Token Exchange [RFC8693] to
obtain a Tx-Token. To do this, it invokes a special Token Service
(the Tx-Token Service) and provides context that is sufficient for it
to generate a Tx-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 Tx-Token Service
to issue the Tx-Token
The Tx-Token Service responds to a successful invocation by
generating a Tx-Token. The calling workload then uses the Tx-Token
to authorize its calls to subsequent workloads. Subsequent workloads
may obtain Tx-Tokens of their own.
2.2.2. Nested Tx-Tokens
A workload within the call chain of such an external call MAY
generate a new Nested Tx-Token. To generate the Nested Tx-Token, it
creates a self-signed JWT Embedded Token [JWTEmbeddedTokens] that
includes the received Tx-Token by value. Subsequent workloads can
therefore know that the signing workload was in the path of the call
chain.
2.3. Tx-Token Lifetime
Tx-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 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 Tx-Token SHALL
still be short-lived.
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2.4. Benefits of Tx-Tokens
Tx-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 Tx-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. Tx-Token Issuance and Usage Flows
Figure 1 shows how Tx-Tokens are used in an a multi-workload
environment.
| (A) Access Token
| via external API
v
+--------------+ (B) Tx-Token Request +---------------+
| Resource |---------------------->| |
| Server | (C) Leaf Tx-Token | Transaction |
| (Workload 1) |<----------------------| Token |
+--------------+ | Server |
| | |
| (D) Send Request | |
| with Leaf Tx-Token | |
| for Workload 1 | |
v | |
+--------------+ | |
| Workload 2 | | |
| | | |
| | | |
+--------------+ | |
| (E) Use unmodified | |
| Leaf Tx-Token | |
| for Workload 1 | |
v | |
+--------------+ | |
| Workload 3 |---+ (F) Create | |
| | | Nested | |
| |<--+ Tx-Token | |
+--------------+ | |
| (G) Send request with | |
| Nested Tx-Token for | |
| Workload 3 | |
v | |
+--------------+ (H) Tx-Token Request | |
| Workload 4 |---------------------->| |
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| | (I) Tx-Token Response | Transaction |
| |<----------------------| Token |
+--------------+ | Server |
| (J) Send request with | |
| Leaf Tx-Token for | |
| Workload 5 | |
: | |
: | |
| | |
| | |
| | |
v | |
+--------------+ | |
| Workload n | (K) Tx-Token verified | |
| | by last workload | |
| | in call chain | |
+--------------+ +---------------+
Figure 1: Use of Tx-Tokens in Multi-Workload Environments
* (A) The user accesses a resource server and present an Access
Token obtained from an Authorization Server using an OAuth 2.0 or
an OpenID Connect flow.
* (B) The resource server is implemented as a workload (Workload 1)
and requests a Leaf Tx-Token from the Transaction Token Server
using the Token Exchange protocol [RFC8693].
* (C) The Transaction Token Service returns a Leaf Tx-Token
containing the requested claims that establish the identity of the
original caller as well as additional claims that can be used to
make authorization decisions and establish the call chain.
* (D) The Resource Server (Workload 1) calls Workload 2 and passes
the Leaf Tx-Token for Workload 1. Workload 2 validates the Tx-
Token and makes an authorization decision by combining contextual
information at its disposal with information in the Tx-Token to
make an authorization decision to accept or reject the call.
* (E) Workload 2 is not required to add aditional information to the
Tx-Token and passes the unmodified Tx-Token for Workload 1 to
Workload 3. Workload 3 validates the Tx-Token and makes an
authorization decision by combining contextual information at its
disposal with information in the Tx-Token to make an authorization
decision to accept or reject the call.
* (F) Workload 3 generates a Nested Tx-Token that includes
additional call chain information.
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* (G) Workload 3 sends the Nested Tx-Token to Workload 4. Workload
4 validates the Nested Tx-Token and makes an authorization
decision by combining contextual information at its disposal with
information in the Nested Tx-Token to make an authorization
decision to accept or reject the call.
* (H) Workload 4 needs a Tx-Token containing information from the
Authroization Server and requests a new Leaf Transaction Token
(Leaf Tx-Token) from the Transaction Token Server using the Token
Exchange protocol [RFC8693].
* (I) The Transaction Token Service returns a Leaf Transaction Token
(Leaf Tx-Token) containing the requested claims that include the
call chain information included in the Tx-Token as well as
additional claims needed.
* (J) Workload 4 sends the Tx-Token to the Workload 5, who verifies
it and extracts claims and combine it with contextual information
for use in authroization decisions. Other workloads continue to
pass Tx-Tokens, generate Nested Tx-Tokens or request new Tx-
Tokens.
* (K) Workload n is the final workload in the call chain. It
verifies the received Tx-Token, extracts claims and combine it
with contextual information for use in authroization decisions.
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 a name that is used as the aud (audience) value
in Tx-Tokens.
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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.
Transaction Token (Tx-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. A Tx-Token may contain a nested Tx-Token.
Leaf Tx-Token: A Tx-Token that does not contain a tx_token claim in
its JWT body.
Nested Tx-Token: A JWT Embedded Token [JWTEmbeddedTokens] that
embeds a Tx-Token by value.
Authorization Context: A JSON object containing a set of claims that
represent the immutable context of a call chain.
Transaction Token Service (Tx-Token Service): A special service
within the Trust Domain, which issues Tx-Tokens to requesting
workloads.
5. Tx-Token Format
A Tx-Token is a JSON Web Token [RFC7519] protected by a JSON Web
Signature [RFC7515]. The following is true in a Tx-Token:
5.1. JWT Header
In the JWT Header:
* The typ claim MUST be present and MUST have the value tx_token.
* Key rotation of the signing key SHOULD be supported through the
use of a kid claim.
Figure 2 is a non-normative example of the JWT Header of a Tx-Token
{
"typ": "tx_token",
"alg": "RS256",
"kid": "identifier-to-key"
}
Figure 2: Example: Tx-Token Header
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5.2. JWT Body
5.2.1. Common Claims
The JWT body MUST have the following claims regardless of whether the
Tx-Token is a Leaf Tx-Token or a Nested Tx-Token:
* An iss claim, whose value is a URN [RFC8141] that uniquely
identifies the workload or the Tx-Token Service that created the
Tx-Token.
* An iat claim, whose value is the time at which the Tx-Token was
created.
* An exp claim, whose value is the time at which the Tx-Token
expires. Note that if this claim is in a Nested Tx-Token, then
this exp value MUST NOT exceed the exp value of the Tx-Token
included in the JWT Body.
5.2.2. Leaf Tx-Token Claims
The following claims MUST be present in the JWT body of a Leaf Tx-
Token:
* A tid claim, whose value is the unique identifier of 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 azc claim, whose value is a JSON object that contains values
that remain constant in the call chain.
Figure 3 shows a non-normative example of the JWT body of a Leaf Tx-
Token:
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{
"iss": "https://trust-domain.example/tx-token-service",
"iat": "1686536226000",
"exp": "1686536526000",
"tid": "97053963-771d-49cc-a4e3-20aad399c312",
"sub_id": {
"format": "email",
"email": "user@trust-domain.example"
},
"azc": {
"action": "BUY", // parameter of external call
"ticker": "MSFT", // parameter of external call
"quantity": "100", // parameter of external call
"user_ip": "69.151.72.123", // env context of external call
"user_level": "vip" // computed value not present in external call
}
}
Figure 3: Example: Leaf Tx-Token Body
5.2.3. Nested Tx-Token Claim
A Nested Tx-Token is a JWT Embedded Token [JWTEmbeddedTokens], which
embeds a Tx-Token by value. The following claims MUST be present in
a Nested Tx-Token:
* A type claim, whose value is urn:ietf:params:oauth:token-
type:tx_token.
* A token claim, whose value is an encoded JWT representation of a
Tx-Token.
Figure 4 shows a non-normative example the JWT body of a nested Tx-
Token
{
"iss": "https://trust-domain.example/fraud-detection",
"iat": "1686536236000",
"exp": "1686536526000",
"type": "urn:ietf:params:oauth:token-type:tx_token",
"token": "eyJ0eXAiOiJ0cmF0Iiwi...thwd8"
}
Figure 4: Example: Nested Tx-Token Body
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6. Requesting Leaf Tx-Tokens
A workload requests a Tx-Token from a Transaction Token Service using
OAuth 2.0 Token Exchange [RFC8693]. The request to obtain a Tx-Token
using this method is called a Tx-Token Request, and a success
response is called a Tx-Token Response. A Tx-Token Request is a
Token Exchange Request, as described in Section 2.1 of [RFC8693] with
additional parameters. A Tx-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 tx_token.
The Transaction Token Service acts as an OAuth 2.0 [RFC6749]
Authorization Server. The requesting workload acts as the OAuth 2.0
Client, which authenticates itself to the Transaction Token Service
through mechanisms defined in OAuth 2.0.
6.1. Tx-Token Request
A Tx-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 is true of the Tx-Token Request:
* The audience value MUST be set to the Trust Domain name.
* The requested_token_type value MUST be
urn:ietf:params:oauth:token-type:tx_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 Tx-Token
Request:
* A parameter named azc , whose value is a JSON object. This object
contains any information the Transaction Token Service needs to
understand the context of the incoming request.
Figure 5 shows a non-normative example of a Tx-Token Request.
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POST /tx-token-service/token_endpoint HTTP 1.1
Host: tx-token-service.trust-domain.example
Content-Type: application/x-www-form-urlencoded
requested_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Atx_token
&audience=http%3A%2F%2Ftrust-domain.example
&subject_token=eyJhbGciOiJFUzI1NiIsImtpZC...kdXjwhw
&subject_token_type=urn%3Aietf%3Aparams%3Aoauth%3Atoken-type%3Aaccess_token
&azc=%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: Tx-Token Request
6.2. Tx-Token Response
A successful response to a Tx-Token Request by a Transaction Token
Service is called a Tx-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 is true of a Tx-Token
Response:
* The token_type value MUST be set to tx_token.
* The access_token value MUST be the Tx-Token.
* The response MUST NOT include the values expires_in, refresh_token
and scope.
Figure 6 shows a non-normative example of a Tx-Token Response.
HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: non-cache, no-store
{
"issued_token_type": "urn:ietf:params:oauth:token-type:tx_token",
"access_token": "eyJCI6IjllciJ9...Qedw6rx"
}
Figure 6: Example: Tx-Token Response
7. Creating Nested Tx-Tokens
A workload within a call chain MAY create a Nested Tx-Token. It does
so by embedding the Tx-Token it receives by value in a JWT Embedded
Token [JWTEmbeddedTokens]. Nested Tx-Tokens are self-signed and not
requested from a separate service.
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The expiration time of a enclosing Tx-Token MUST NOT exceed the
expiration time of an embedded Tx-Token.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
9.1. Mutual Authentication of the Tx-Token Request
A Transaction Token Service MUST ensure that it authenticates any
workloads requesting Tx-Tokens. In order to do so:
* It MUST name a limited, pre-configured set of workloads that MAY
request Tx-Tokens.
* It MUST individually authenticate the requester as being one of
the name requesters.
* It SHOULD rely on mechanisms, such as [Spiffe], 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 Tx-Token Request.
9.2. Sender Constrained Tokens
Although Tx-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.
9.3. Access Tokens
When creating Tx-Tokens, the Tx-Token MUST NOT contain the Access
Token presented to the resource server. If an Access Token is
included in a Tx-Token, an attacker may obtain a Tx-Token, extract
the Access Token, and replay it to the Resource Server. Tx-Token
expiry does not protect against this attack since the Access Token
may remain valid even after the Tx-Token has expired.
10. References
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10.1. 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/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>.
[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>.
[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/info/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/info/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/info/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/info/rfc8693>.
[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>.
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[JWTEmbeddedTokens]
Shekh-Yusef, R., Hardt, D., and G. D. Marco, "JSON Web
Token (JWT) Embedded Tokens", n.d.,
<https://www.ietf.org/archive/id/draft-yusef-oauth-nested-
jwt-06.html>.
10.2. 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
Evan Gilman
SPIRL
Email: evan@spirl.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
Pieter Kasselman
Microsoft
Email: pieter.kasselman@microsoft.com
Tulshibagwale, et al. Expires 8 January 2024 [Page 15]