AuthZEN Request/Response Profile for OAuth 2.0 Rich Authorization Requests

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Table of Contents

1. Introduction

OpenID AuthZEN is a Working Group under the OpenID Foundation which aims to increase interoperability and standardization in the authorization realm. In particular, AuthZEN aims to:¶

• build standards-based authorization APIs¶

• define standard design patterns for authorization¶

• produce educational material to help raise awareness of externalized authorization.¶

The aim of this profile is to define an AuthZEN-conformant profile of the OAuth 2.0 Rich Authorization Requests [RFC9396]. [RFC9396] introduces a new parameter authorization_details that allows clients to specify their fine-grained authorization requirements using the expressiveness of JSON [RFC8259] data structures. This specification introduces a more structured format for the authorization_details parameter. The new format is also JSON [RFC8259] as a result of which this specification is conformant with [RFC9396] and is merely a stricter profile.¶

For example the authorization request for a credit transfer mentioned in [RFC9396] would now be structured as follows¶

{
    "subject": {
        "type": "user",
        "id": "Alice"
    },
    "resource": {
        "type": "payment_initiation",
        "id": "123",
        "recipient": {
            "creditorName": "Merchant A",
            "creditorAccount": {
                "bic": "ABCIDEFFXXX",
                "iban": "DE02100100109307118603"
            }
        }
    },
    "action": {
        "name": "transfer",
        "instructedAmount": {
            "currency": "EUR",
            "amount": "123.50"
        }
    },
    "context": {
        "remittance": "Ref Number Merchant"
    }
}

Using AuthZEN as a format for authorization_details will increase the usability and the interoperability of [RFC9396]. In particular, it will be possible for the AS to forward the contents of the authorization_details parameter to an AuthZEN-conformant Policy Decision Point (PDP).¶

2. Conventions and Definitions

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.¶

This specification uses the terms "access token", "refresh token", "authorization server" (AS), "resource server" (RS), "authorization endpoint", "authorization request", "authorization response", "token endpoint", "grant type", "access token request", "access token response", and "client" defined by "The OAuth 2.0 Authorization Framework" [RFC6749]. This specification uses the terms "PDP" and "PEP" defined by [ABAC] and [XACML].¶

3. Request Parameter authorization_details

In [RFC9396], the request parameter authorization_details contains, in JSON notation, an array of objects. Each JSON object contains the data to specify the authorization requirements for a certain type of resource. This specification defines the format for each one of these objects such that it conforms to [AUTHZEN] and [RFC9396].¶

[AUTHZEN] groups JSON datastructures into 4 JSON objects:¶

• subject: A Subject is the user or robotic principal about whom the Authorization API is being invoked. The Subject may be requesting access at the time the Authorization API is invoked.¶

• resource: A Resource is the target of an access request. It is a JSON ([RFC8259]) object that is constructed similar to a Subject entity.¶

• action: An Action is the type of access that the requester intends to perform. Action is a JSON ([RFC8259]) object that contains at least a name field.¶

• context: The Context object is a set of attributes that represent environmental or contextual data about the request such as time of day. It is a JSON ([RFC8259]) object.¶

Note: the aforementioned is indicative only. Always refer to [AUTHZEN] for the formal definition of each element.¶

4. Authorization Request

Conformant to [RFC9396], the authorization_details authorization request parameter can be used to specify authorization requirements in all places where the scope parameter is used for the same purpose, examples include:¶

• authorization requests as specified in [RFC6749]¶

• device authorization requests as specified in [RFC8628]¶

• backchannel authentication requests as defined in [OID-CIBA]¶

Parameter encoding follows the exact same rules as [RFC9396].¶

{
  "type": "authzen_evaluation",
  "request":
    {
        "subject": {
            "type": "user",
            "id": "Alice"
        },
        "resource": {
            "type": "payment_initiation",
            "id": "123",
            "recipient": {
                "creditorName": "Merchant A",
                "creditorAccount": {
                    "bic": "ABCIDEFFXXX",
                    "iban": "DE02100100109307118603"
                }
            }
        },
        "action": {
            "name": "transfer",
            "instructedAmount": {
                "currency": "EUR",
                "amount": "123.50"
            }
        },
        "context": {
            "remittance": "Ref Number Merchant"
        }
    }
}

5. Support for Multiple Authorization Requests

[AUTHZEN] supports a profile that allows the expression of multiple authorization requests in a single JSON object. As a result, this profile recommends the use of a single authorization_details object containing boxcarred requests as described in [BOXCAR] when possible and the use of the authorization_details array otherwise.¶

[
  {
    "type": "authzen_evaluations",
    "request":
    {
      "subject": {
        "id": "alice@acmecorp.com",
        "type": "user"
      },
      "resource":{
        "id": "123",
        "type": "account_information",
        "location": "https://example.com/accounts"
      },
      "evaluations": {
        "eval-1": {
          "action": {
            "name": "list_accounts"
          }
        },
        "eval-2": {
          "action": {
            "name": "read_balances"
          }
        },
        "eval-3": {
          "action": {
            "name": "read_transactions"
          }
        }
      }
    }
  },
  {
    "type": "authzen_evaluations",
    "request":
    {
      "subject": {
        "id": "alice@acmecorp.com",
        "type": "user"
      },
      "resource":{
        "id": "123",
        "type": "payment_initiation",
        "location": "https://example.com/payments",
        "recipient": {
            "creditorName": "Merchant A",
            "creditorAccount": {
                "bic": "ABCIDEFFXXX",
                "iban": "NL02RABO2228161411"
            }
        }
      },
      "context":{
        "remittance": "Ref Number Merchant"
      },
      "evaluations": {
        "eval-1": {
          "action": {
            "name": "initiate",
            "instructedAmount": {
            "currency": "EUR",
            "amount": "123.50"
            }
          }
        },
        "eval-2": {
          "action": {
            "name": "status"
          }
        },
        "eval-3": {
          "action": {
            "name": "cancel"
          }
        }
      }
    }
  }
]

6. Authorization Responses

Whereas [RFC9396] doesn't specify any extensions for authorization_details responses, [AUTHZEN] standardizes the responses expected from the PDP. An AuthZEN response is therefore expected for all AuthZEN requests. This response can be used by authorization clients directly or by the AS during token creation. In particular, authorization response can be used in conjunction with any user-consent flow.¶

The new authorization_details response structure is as follows:¶

• type: The value of this field is expected to be "authzen_evaluation" for a single authorization request, or "authzen_evaluations" for multiple (Boxcarred) evalution requests. This field is REQUIRED.¶

• response: This field contains the entire AuthZEN-conformant authorization response. This field is REQUIRED.¶

[
  {
    "type": "authzen_evaluation",
    "response": {
        "decision": true
    }
  }
]

[
  {
    "type": "authzen_evaluations",
    "response": {
      "evaluations": {
        "eval-1": {
          "decision": true
        },
        "eval-2": {
          "decision": false,
          "context": {
            "reason": "resource not found"
          }
        },
        "eval-3": {
          "decision": false,
          "context": {
            "reason": "Subject is a viewer of the resource"
          }
        }
      }
    }
  },
  {
    "type": "authzen_evaluations",
    "response": {
      "evaluations": {
        "eval-1": {
          "decision": true
        },
        "eval-2": {
          "decision": false,
        },
        "eval-3": {
          "decision": false,
            "context": {
              "error": {
                "status": 404,
                "message": "Resource not found"
            }
          }
        }
      }
    }
  }
]

7. Security Considerations

The Security Considerations of [RFC9396], [RFC6749], [RFC7662], and [RFC8414] all apply.¶

8. IANA Considerations

This document has no IANA actions.¶

Acknowledgments

We would like to thank members of the OpenID AuthZEN Working Group for their valuable feedback during the preparation of this specification. In particular our thanks go to Gerry Gebel and Allan Foster.¶

We would also like to thank Justin Richer and Pieter Kasselman for their guidance on this spec and the overall IETF process.¶

Authors' Addresses