fapi-2-advanced May 2022
Fett & Tonge Standards Track [Page]
Workgroup:
fapi
Internet-Draft:
fapi-2_0-advanced-00
Published:
Intended Status:
Standards Track
Authors:
D. Fett
yes.com
D. Tonge
Moneyhub Financial Technology

FAPI 2.0 Advanced Profile

Abstract

OIDF FAPI 2.0 is an API security profile based on the OAuth 2.0 Authorization Framework [RFC6749].

Table of Contents

1. Introduction

1.1. Warning

This document is not an OIDF International Standard. It is distributed for review and comment. It is subject to change without notice and may not be referred to as an International Standard.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to provide supporting documentation.

1.3. Notational Conventions

The keywords "shall", "shall not", "should", "should not", "may", and "can" in this document are to be interpreted as described in ISO Directive Part 2 [ISODIR2]. These keywords are not used as dictionary terms such that any occurrence of them shall be interpreted as keywords and are not to be interpreted with their natural language meanings.

2. Advanced Profile

OIDF FAPI is an API security profile based on the OAuth 2.0 Authorization Framework [RFC6749]. This Advanced Profile aims to reach the security goals and the non-repudiation goals laid out in the Attacker Model [attackermodel].

All provisions of the [Baseline Profile] apply to the Advanced Profile as well, with the extensions described in the following.

2.1. Profile

In addition to the technologies used in the [Baseline Profile], the following standards are used in the Advanced Profile:

We understand that some ecosystems may only desire to implement 1 or 2 of the above 3, it is therefore anticipated that a piece of software will be able to conform to each of the methods separately, i.e. there will be separate tests for the following:

  • FAPI2Advanced-JAR

  • FAPI2Advanced-JARM

  • FAPI2Advanced-JIR

  • FAPI2Advanced-HTTPSig

2.1.1. Signing Authorization Requests

2.1.1.1. Requirements for Authorization Servers

Authorization servers implementing FAPI2 authorization request signing

  1. shall support and verify signed request objects according to JAR [RFC9101] at the PAR endpoint [RFC9126]

  2. shall require the aud claim in the request object to be, or to be an array containing, the OP's Issuer Identifier URL;

  3. shall require the request object to contain an nbf claim that is no longer than 60 minutes in the past; and

  4. shall require the request object to contain an exp claim that has a lifetime of no longer than 60 minutes after the nbf claim;

2.1.1.2. Requirements for Clients

Clients implementing FAPI2 authorization request signing

  1. shall sign request objects according to JAR [RFC9101] that are sent to the PAR endpoint [RFC9126]

  2. shall send the aud claim in the request object as the OP's Issuer Identifier URL;

  3. shall send a nbf claim in the request object;

  4. shall send an exp claim in the request object that has a lifetime of no longer than 60 minutes;

2.1.2. Signing Authorization Responses

2.1.2.1. Requirements for Authorization Servers

Authorization servers implementing FAPI2 authorization response signing

  1. shall support and issue signed authorization responses via JWT Secured Authorization Response Mode for OAuth 2.0 [JARM]

2.1.2.2. Requirements for Clients

Clients implementing FAPI2 authorization response signing

  1. shall set the response_mode to jwt in the authorization request as defined in [JARM]

  2. shall verify signed authorization responses according to [JARM]

2.1.3. Signing Introspection Responses

2.1.3.1. Requirements for Authorization Servers

Authorization servers implementing FAPI2 introspection response signing

  1. shall sign introspection responses that are issued in JWT format according to [I-D.ietf-oauth-jwt-introspection-response]

2.1.3.2. Requirements for Clients

Clients implementing FAPI2 introspection response signing

  1. shall request signed token introspection responses according to [I-D.ietf-oauth-jwt-introspection-response]

  2. shall verify the signed token introspection responses

2.1.4. HTTP Message Signing

This profile supports HTTP Message Signing using the HTTP Message Signatures specification being developed by the IETF HTTP Working Group.

2.1.4.1. Requirements for Clients

Clients implementing HTTP Message Signing

  1. shall create an HTTP Message Signature as described in [I-D.ietf-httpbis-message-signatures].

  2. shall include @method (the method used in the HTTP request) in the signature input

  3. shall include @target-uri (the full request URI of the HTTP request) in the signature input

  4. when the message contains a request body, include the content-digest header as defined in [I-D.ietf-httpbis-digest-headers] in the request, and include that header in the signature input. Content-encoding agnostic digest methods (such as sha-256) should be used.

  5. shall accept and verify the signature in the response as described in [I-D.ietf-httpbis-message-signatures]

2.1.4.2. Requirements for Resource Servers

The FAPI 2.0 endpoints are OAuth 2.0 protected resource endpoints that perform sensitive actions and return protected information for the resource owner associated with the submitted access token.

Resource servers with FAPI endpoints implementing HTTP Message Signing

  1. shall verify the signature received from the Client as described in [I-D.ietf-httpbis-message-signatures].

  2. shall reject requests with missing or invalid signatures using HTTP Status Code 401

  3. shall create an HTTP Message Signature for the response as described in [I-D.ietf-httpbis-message-signatures].

  4. shall cryptographically link the response to the request using @request-response in the signature input as defined in 2.2.11 in [I-D.ietf-httpbis-message-signatures]

  5. shall include the content-digest header as defined in [I-D.ietf-httpbis-digest-headers] in the response, and include that header in the signature input. Content-encoding agnostic digest methods (such as sha-256) should be used.

  6. shall include @status (the status code of the response) in the signature input

2.2. MTLS Protection of all endpoints

Some ecosystems are choosing to require clients accessing their endpoints to supply a TLS client certificate at endpoints that would not otherwise require a TLS client certificate (for example, the PAR endpoint when using privatekeyjwt authentication).

This is outside of the scope of both [RFC8705] and the FAPI standards, however in the interests of interoperability we state that when using TLS as a transport level protection in this manner, authorization servers should expect clients to call the endpoints located in the root of the server metadata, and not those found in mtls_endpoint_aliases.

3. Normative References

[JARM]
Lodderstedt, T. and B. Campbell, "Financial-grade API: JWT Secured Authorization Response Mode for OAuth 2.0 (JARM)", , <https://openid.net/specs/openid-financial-api-jarm.html>.
[RFC7662]
Richer, J., Ed., "OAuth 2.0 Token Introspection", RFC 7662, DOI 10.17487/RFC7662, , <https://www.rfc-editor.org/info/rfc7662>.
[RFC9126]
Lodderstedt, T., Campbell, B., Sakimura, N., Tonge, D., and F. Skokan, "OAuth 2.0 Pushed Authorization Requests", RFC 9126, DOI 10.17487/RFC9126, , <https://www.rfc-editor.org/info/rfc9126>.
[RFC8705]
Campbell, B., Bradley, J., Sakimura, N., and T. Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens", RFC 8705, DOI 10.17487/RFC8705, , <https://www.rfc-editor.org/info/rfc8705>.
[RFC6749]
Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, , <https://www.rfc-editor.org/info/rfc6749>.
[ISODIR2]
Standardization, I. O. F., "ISO/IEC Directives Part 2 -", , <https://www.iso.org/sites/directives/current/part2/index.xhtml>.
[attackermodel]
Fett, D., "FAPI 2.0 Attacker Model", , <https://bitbucket.org/openid/fapi/src/master/FAPI_2_0_Attacker_Model.md>.
[RFC9101]
Sakimura, N., Bradley, J., and M. Jones, "The OAuth 2.0 Authorization Framework: JWT-Secured Authorization Request (JAR)", RFC 9101, DOI 10.17487/RFC9101, , <https://www.rfc-editor.org/info/rfc9101>.

4. Informative References

[I-D.ietf-httpbis-message-signatures]
Backman, A., Richer, J., and M. Sporny, "HTTP Message Signatures", Work in Progress, Internet-Draft, draft-ietf-httpbis-message-signatures-09, , <https://tools.ietf.org/html/draft-ietf-httpbis-message-signatures-09>.
[I-D.ietf-oauth-jwt-introspection-response]
Lodderstedt, T. and V. Dzhuvinov, "JWT Response for OAuth Token Introspection", Work in Progress, Internet-Draft, draft-ietf-oauth-jwt-introspection-response-12, , <https://tools.ietf.org/html/draft-ietf-oauth-jwt-introspection-response-12>.

Authors' Addresses

Daniel Fett
yes.com
Dave Tonge
Moneyhub Financial Technology