Raw-Public-Key and Pre-Shared-Key as OAuth client credentials
draft-erdtman-ace-rpcc-01

Abstract

This document describes Transport Layer Security (TLS) authentication using Raw-Public-Key and Pre-Shared-Key as new mechanisms for OAuth client authentication. Although defined for TLS the mechanisms are equally applicable for DTLS.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on February 18, 2018.

Copyright Notice

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Table of Contents

• 1. Introduction
• 1.1. Requirements Language
• 2. Pre-Shared-Key for Client Authentication
• 3. Raw-Public-Key for Client Authentication
• 4. Acknowledgements
• 5. IANA Considerations
• 5.1. Token Endpoint Authentication Method Registration
• 5.1.1. Registry Contents
• 5.1.2. Registry Contents
• 6. Security Considerations
• 7. References
• 7.1. Normative References
• 7.2. Informative References
• Authors' Addresses

1. Introduction

This document describes Transport Layer Security (TLS) authentication using Raw-Public-Key and Pre-Shared-Key as the mechanism for OAuth client authentication. Examples of endpoint requiering client authentication are token and introspection.

The OAuth 2.0 Authorization Framework [RFC6749] defines a shared secret method of client authentication but also allows for the definition and use of additional client authentication mechanisms when interacting with the authorization server's token endpoint. This document describes two additional mechanisms of client authentication utilizing Raw-Public-Key [RFC7250] and Pre-Shared-Key TLS [RFC4279], which provide better security characteristics than shared secrets.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

2. Pre-Shared-Key for Client Authentication

The following section defines, as an extension of OAuth 2.0, Section 2.3, using Pre-Shared-Key with TLS [RFC4279] to authenticate the client. This method is registered as 'tls_client_psk' in "OAuth Token Endpoint Authentication Methods" registry.

The (D)TLS handshake MUST be done according to [RFC4279], with the client indicating support for one or more Pre-Shared-Key cipher suites and authorization server selecting a Pre-Shared-Key cipher suite. In order to enable authorization server to select the correct pre-shared-key the client MUST send its client identifier in the psk-identity field of the ClientKeyExchange message. How the authorization server maps a client identifier to the pre-shared-key is out of scope for this specification.

Note that the client identity MUST be 2^16 bytes or shorter, in order to fit into the psk-identity field.

3. Raw-Public-Key for Client Authentication

The following section defines, as an extension of OAuth 2.0, Section 2.3, the use of Raw-Public-Key with (D)TLS [RFC7250] to authenticate the client. This method is registered as'tls_client_rpk' in "OAuth Token Endpoint Authentication Methods" registry.

The (D)TLS handshake MUST be done according to [RFC7250], with the client indicating support for Raw-Public-Key certificates and the authorization server asking client send its Raw Public Key certificate. Since the client cannot send an explicit client identifier in the handshake, the authorization server MUST the derive a client identifier from RPK that the client uses.

         Raw Public Key (Base64 encoded):
         MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEEtboxNKPgxEKV9JTNzy
         tUvAbxEfkCTVB9kOzheF5wRAoOz2NKP+ln+XLVAQSp1D6jfo09tppvN
         poQA1nnBNH6A==";

         Encoding:
         ni:///sha-256;xzLa24yOBeCkos3VFzD2gd83Urohr9TsXqY9nhdDN0
         

Figure 1: Example encoding of a raw public key in the Named Information URI Format

Authorization servers MAY use the following method to map a Raw Public Key to a client identifier: The client identifier is generated from the Raw Public Key using the procedure specified in section 3 of. The digest is calculated on the Raw Public Key only (not on the SubjectPublicKeyInfo used in the handshake). An example is shown in Figure 1.

4. Acknowledgements

This document is highly inspired by [I-D.ietf-oauth-mtls] written by B. Campbell, J. Bradley, N. Sakimura and T. Lodderstedt.

5. IANA Considerations

5.1. Token Endpoint Authentication Method Registration

This specification requests registration of the following value in the IANA "OAuth Token Endpoint Authentication Methods" registry [IANA.OAuth.Parameters] established by [RFC7591].

5.1.1. Registry Contents

• Token Endpoint Authentication Method Name: tls_client_rpk
• Change Controller: IESG
• Specification Document(s): [[ this specification ]]

5.1.2. Registry Contents

• Token Endpoint Authentication Method Name: tls_client_psk
• Change Controller: IESG
• Specification Document(s): [[ this specification ]]

6. Security Considerations

TBD

7. References

7.1. Normative References

7.2. Informative References

Authors' Addresses