OAuth Working Group M. Jones
Internet-Draft Microsoft
Intended status: Standards Track P. Hunt
Expires: January 23, 2016 Oracle
July 22, 2015

Authentication Method Reference Values
draft-jones-oauth-amr-values-00

Abstract

The amr (Authentication Methods References) claim is defined and registered in the IANA "JSON Web Token Claims" registry but no standard Authentication Method Reference values are currently defined. This specification establishes a registry for Authentication Method Reference values and defines an initial set of Authentication Method Reference values. It also defines the amr_values (requested Authentication Method Reference values) request parameter for requesting that a set of Authentication Method Reference values be used for processing the Authentication Request.

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Table of Contents

1. Introduction

The amr (Authentication Methods References) claim is defined and registered in the IANA "JSON Web Token Claims" registry [IANA.JWT.Claims] but no standard Authentication Method Reference values are currently defined. This specification establishes a registry for Authentication Method Reference values and defines an initial set of Authentication Method Reference values. It also defines the amr_values (requested Authentication Method Reference values) request parameter for requesting that a set of Authentication Method Reference values be used for processing the Authentication Request.

1.1. Requirements Notation and 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 RFC 2119 [RFC2119].

1.2. Terminology

This specification uses the terms defined by JSON Web Token (JWT) [JWT] and OpenID Connect Core 1.0 [OpenID.Core].

2. Authentication Method Reference Values

The amr (Authentication Methods References) claim is defined by the OpenID Connect Core 1.0 specification [OpenID.Core] as follows:

amr

OPTIONAL. Authentication Methods References. JSON array of strings that are identifiers for authentication methods used in the authentication. For instance, values might indicate that both password and OTP authentication methods were used. The definition of particular values to be used in the amr Claim is beyond the scope of this specification. Parties using this claim will need to agree upon the meanings of the values used, which may be context-specific. The amr value is an array of case sensitive strings.

However, OpenID Connect does not specify any particular Authentication Method Reference values to be used in the amr claim. The following is a list of Authentication Method Reference values defined by this specification:

pwd

Password authentication, either by the user or the service if a client secret is used
pop

Proof of possession of a key
otp

One time password
fpt

Fingerprint biometric
eye

Retina scan biometric
vbm

Voice biometric
tel

Confirmation by telephone call
sms

Confirmation by SMS reply
kba

Knowledge based authentication
wia

Windows integrated authentication
mfa

Multiple factor authentication. When this is present, the other authentication methods used will also be included.

3. Authentication Request Parameter

This section defines the following authentication request parameter, augmenting the set of authentication request parameters defined in Section 3.1.2.1 of OpenID Connect Core 1.0 [OpenID.Core]:

amr_values

OPTIONAL. Requested Authentication Method Reference values. Space-separated string that specifies the amr values that the Authorization Server is being requested to use for processing this Authentication Request, with the values appearing in order of preference. The authentication methods used for the authentication performed are returned as the amr Claim Value.

4. Relationship to "acr" (Authentication Context Class Reference)

The acr (Authentication Context Class Reference) claim and acr_values request parameter are related to the amr (Authentication Methods References) claim and amr_values request parameter, but with important differences. Authentication Context Classes specify a set of business rules that authentications are being requested to satisfy. These rules can often be satisfied by using a number of different specific authentication methods, either singly or in combination. Interactions using acr request that specified Authentication Context Classes be used and reply saying which Authentication Context Class was satisfied. The reply states that it was satisfied -- not how it was satisfied.

In contrast, interactions using amr make statements about the particular authentication methods that are used. This tends to be more brittle than using acr since the authentication methods that may be appropriate for a given authentication will vary over time, both because of the evolution of attacks on existing methods and the creation of new authentication methods.

5. Privacy Considerations

The list of amr claim values returned in an ID Token reveals information about the way that the end-user authenticated to the identity provider. In some cases, this information may have privacy implications.

6. Security Considerations

The security considerations in OpenID Connect Core 1.0 [OpenID.Core], OAuth 2.0 [RFC6749], and the OAuth 2.0 Threat Model [RFC6819] apply to this specification.

As described in Section 4, taking a dependence upon particular authentication methods may result in brittle systems, since the authentication methods that may be appropriate for a given authentication will vary over time.

7. IANA Considerations

7.1. Authentication Method Reference Values Registry

This specification establishes the IANA "Authentication Method Reference Values" registry for amr claim array element values. The registry records the Authentication Method Reference value and a reference to the specification that defines it. This specification registers the Authentication Method Reference values defined in Section 2.

Values are registered on a Specification Required [RFC5226] basis after a three-week review period on the jwt-reg-review@ietf.org mailing list, on the advice of one or more Designated Experts. However, to allow for the allocation of values prior to publication, the Designated Experts may approve registration once they are satisfied that such a specification will be published.

Registration requests sent to the mailing list for review should use an appropriate subject (e.g., "Request to register Authentication Method Reference value: otp").

Within the review period, the Designated Experts will either approve or deny the registration request, communicating this decision to the review list and IANA. Denials should include an explanation and, if applicable, suggestions as to how to make the request successful. Registration requests that are undetermined for a period longer than 21 days can be brought to the IESG's attention (using the iesg@ietf.org mailing list) for resolution.

Criteria that should be applied by the Designated Experts includes determining whether the proposed registration duplicates existing functionality, whether it is likely to be of general applicability or whether it is useful only for a single application, and whether the registration description is clear.

IANA must only accept registry updates from the Designated Experts and should direct all requests for registration to the review mailing list.

It is suggested that the same Designated Experts evaluate these registration requests as those who evaluate registration requests for the IANA "JSON Web Token Claims" registry [IANA.JWT.Claims].

7.1.1. Registration Template

Authentication Method Reference Name:

The name requested (e.g., "otp"). Because a core goal of this specification is for the resulting representations to be compact, it is RECOMMENDED that the name be short -- that is, not to exceed 8 characters without a compelling reason to do so. This name is case sensitive. Names may not match other registered names in a case-insensitive manner unless the Designated Experts state that there is a compelling reason to allow an exception.
Authentication Method Reference Description:

Brief description of the Authentication Method Reference (e.g., "One time password").
Change Controller:

For Standards Track RFCs, state "IESG". For others, give the name of the responsible party. Other details (e.g., postal address, email address, home page URI) may also be included.
Specification Document(s):

Reference to the document or documents that specify the parameter, preferably including URIs that can be used to retrieve copies of the documents. An indication of the relevant sections may also be included but is not required.

7.1.2. Initial Registry Contents

7.2. OAuth Parameters Registration

This section registers the following parameter in the IANA "OAuth Parameters" registry [IANA.OAuth.Parameters] established in RFC 6749 [RFC6749].

7.2.1. Registry Contents

8. References

8.1. Normative References

[IANA.JWT.Claims] IANA, "JSON Web Token Claims"
[IANA.OAuth.Parameters] IANA, "OAuth Parameters"
[JWT] Jones, M., Bradley, J. and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, May 2015.
[OpenID.Core] Sakimura, N., Bradley, J., Jones, M., de Medeiros, B. and C. Mortimore, "OpenID Connect Core 1.0", November 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008.
[RFC6749] Hardt, D., "The OAuth 2.0 Authorization Framework", RFC 6749, DOI 10.17487/RFC6749, October 2012.

8.2. Informative References

[RFC6819] Lodderstedt, T., McGloin, M. and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013.

Appendix A. Document History

[[ to be removed by the RFC editor before publication as an RFC ]]

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Authors' Addresses

Michael B. Jones Microsoft EMail: mbj@microsoft.com URI: http://self-issued.info/
Phil Hunt Oracle EMail: phil.hunt@yahoo.com