An AuthZEN profile for trust registries

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Table of Contents

1. Introduction

Technical trust in systems using asymmetric cryptography often involves binding a name to a public key. One such example is, given an X.509 certificate (as a representative of a public key and name), determining its validity relative to a set of trust anchors by means of PKIX path construction and path validation. In this example the trust registry is the set of trust anchors together with the rules for path validation and construction set down in [RFC5280].¶

The proliferation of distributed identity systems have led to the development of a multitude of trust registries each with their own APIs for querying the registry and rules for evaluating trust. Application developers are often faced with the choice of choosing one of these trust registries which leads to interoperability problems. It is often common for an service to register with multiple trust registries in order to reach all intended audiences.¶

This document describes an API for trust evaluation that is intended to fill a role similar to the stub resolver in the DNS architecture. The API is defined as a profile of [AUTHZEN]. AuthZen is a proposed standard for communicating between an authorization policy enforcement point (PEP) and a 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 "PDP" and "PEP" defined by [NIST.SP.800-162] and [XACML]. A trust registry refers to any service that provides a binding (or mapping) between public keys and names. This is referred to as "name to key" or name-to-key binding.¶

3. Endpoints

Implementations of this specification MUST provide the /evaluation endpoint and SHOULD also provide the /evaluations and discovery endpoints. The /search endpoint MAY be provided but providing this endpoint may provide significant challenges for this profile and clients MUST NOT assume that it is present.¶

4. Authorization Request

This profile implements the following semantic: The client (PEP) requests that the server (PDP) authorizes the binding between the name specified by the Subject with the public key specified by the Resource. Optionally the Action is used to constrain the authorization to a specific role that the entity that the public key is bound to must have for the authorization to be approved.¶

5. Authorization Response

This profile does not constrain or profile the standard response message format. An implementation MAY choose to provide detailed error messages or other contextual information as per the AuthZen specification.¶

6. Examples (non-normative)

The following example is a query to check if a provided certificate chain is bound to the name "did:foo:bla" and is allowed act as a EUDI wallet provider.¶

{
  "type": "authzen",
  "request": {
      "subject": {
        "type": "key",
        "id": "did:foo:bla"
    },
    "resource": {
      "type": "x5c",
      "id": "did:foo:bla",
      "key": ["... x5c data ..."]
    },
    "action": {
      "name": "http://ec.europa.eu/NS/wallet-provider",
    }
  }
}

The following example is a query to check if a provided certificate chain is bound to "www.example.com" and is allowed to act as a TLS server.¶

{
  "type": "authzen",
  "request": {
      "subject": {
        "type": "key",
        "id": "www.example.com"
    },
    "resource": {
      "type": "x5c",
      "id": "www.example.com",
      "key": ["... x5c data ..."],
    },
    "action": {
      "name": "TODO:oid:tls-server",
    }
  }
}

The following is an example response with no additional context:¶

{
  "decision": true
}

The following is an hypothetical response with error messages:¶

{
  "decision": false,
  "context": {
    "reason": {
      "403": "Unknown service - contact helpdesk@registry.example.com for support using the following identifier: #ID4711"
    }
  }
}

7. Security Considerations

The protocol described in this specification is meant to be used by applications that share a common security domain and it may be perfectly reasonable for deployments of this specification to be deployed without authentication on "localhost" or in situations where security requirements for the protocol is provided elsewhere in the stack. In general implementations of this specification MAY implement [RFC6749] authentication for the purpose of authenticating the client (PDP) to the server (PEP) and SHOULD provide a way for the PDP to be authenticated to the client.¶

In addition to the above the security considerations for authentication for AuthZen applies in equal measure to this profile.¶

8. IANA Considerations

This document has no IANA actions.¶

9. References

Acknowledgments

TODO acknowledge.¶

Author's Address