|OAuth Working Group||M. Jones|
|Intended status: Standards Track||P. Hunt|
|Expires: September 14, 2017||Oracle|
|March 13, 2017|
Authentication Method Reference Values
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.
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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.
For context, the amr (Authentication Methods References) claim is defined by Section 2 of the OpenID Connect Core 1.0 specification [OpenID.Core] as follows:
Each amr value typically provides an identifier for a family of closely-related authentication methods. For example, the otp identifier intentionally covers both time-based and HMAC-based OTPs. Many relying parties will be content to know that an OTP has been used in addition to a password; the distinction between which kind of OTP was used is not useful to them. Thus, there's a single identifier that can be satisfied in two or more nearly equivalent ways.
Similarly, there's a whole range of nuances between different fingerprint matching algorithms. They differ in false positive and false negative rates over different population samples and also differ based on the kind and model of fingerprint sensor used. Like the OTP case, many relying parties will be content to know that a fingerprint match mas made, without delving into and differentiating based on every aspect of the implementation of fingerprint capture and match. The fpt identifier accomplishes this.
Ultimately, the relying party is depending upon the identity provider to do reasonable things. If it does not trust the identity provider to do so, it has no business using it. The amr value lets the identity provider signal to the relying party additional information about what it did, for the cases in which that information is useful to the relying party.
The amr values defined by this specification are not intended to be an exhaustive set covering all use cases. Additional values can and will be added to the registry by other specifications. Rather, the values defined herein are an intentionally small set that are already actually being used in practice.
The values defined by this specification only make distinctions that are known to be useful to relying parties. Slicing things more finely than would be used in practice would actually hurt interop, rather than helping it, because it would force relying parties to recognize that several or many different values actually mean the same thing to them.
For context, while the claim values registered pertain to authentication, note that OAuth 2.0 [RFC6749] is designed for resource authorization and cannot be used for authentication without employing appropriate extensions, such as those defined by OpenID Connect Core 1.0 [OpenID.Core]. The existence of the amr claim and values for it should not be taken as encouragement to try to use OAuth 2.0 for authentication without employing extensions enabling secure authentication to be performed.
When used with OpenID Connect, if the identity provider supplies an amr claim in the ID Token resulting from a successful authentication, the relying party can inspect the values returned and thereby learn details about how the authentication was performed. For instance, the relying party might learn that only a password was used or it might learn that iris recognition was used in combination with a hardware-secured key. Whether amr values are provided and which values are understood by what parties are both beyond the scope of this specification. The OpenID Connect MODRNA Authentication Profile 1.0 [OpenID.MODRNA] is one example of an application context that uses amr values defined by this specification.
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].
This specification uses the terms defined by JSON Web Token (JWT) [JWT] and OpenID Connect Core 1.0 [OpenID.Core].
The following is a list of Authentication Method Reference values defined by this specification:
The acr (Authentication Context Class Reference) claim and acr_values request parameter are related to the amr (Authentication Methods References) claim, but with important differences. An Authentication Context Class specifies 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_values request that the specified Authentication Context Classes be used and that the result should contain an acr claim saying which Authentication Context Class was satisfied. The acr claim in the reply states that the business rules for the class were satisfied -- not how they were satisfied.
In contrast, interactions using the amr claim make statements about the particular authentication methods that were 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 deployment of new authentication methods.
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.
While this specification defines identifiers for particular kinds of credentials, it does not define how these credentials are stored or protected. For instance, ensuring the security and privacy of biometric credentials that are referenced by some of the defined Authentication Method Reference values is beyond the scope of this specification.
The security considerations in OpenID Connect Core 1.0 [OpenID.Core] and OAuth 2.0 [RFC6749] and the OAuth 2.0 Threat Model [RFC6819] apply to applications using this specification.
As described in Section 3, 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.
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 an Expert Review [RFC5226] basis after a three-week review period on the firstname.lastname@example.org mailing list, on the advice of one or more Designated Experts. To increase potential interoperability, the experts are requested to encourage registrants to provide the location of a publicly-accessible specification defining the values being registered, so that their intended usage can be more easily understood.
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 email@example.com mailing list) for resolution.
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].
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, whether the value is actually being used, and whether the registration description is clear.
|[IANA.JWT.Claims]||IANA, "JSON Web Token Claims"|
|[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.|
|[ISO29115]||International Organization for Standardization, "ISO/IEC 29115:2013 -- Information technology - Security techniques - Entity authentication assurance framework", ISO/IEC 29115:2013, April 2013.|
|[JECM]||Williamson, G., "Enhanced Authentication In Online Banking", Journal of Economic Crime Management 4.2: 18-19, 2006.|
|[MCA]||ldapwiki.com, "Multiple-channel Authentication", August 2016.|
|[MSDN]||Microsoft, "Integrated Windows Authentication with Negotiate", September 2011.|
|[NIST.800-63-2]||National Institute of Standards and Technology (NIST), "Electronic Authentication Guideline", NIST Special Publication 800-63-2, August 2013.|
|[OpenID.MODRNA]||Connotte, J. and J. Bradley, "OpenID Connect MODRNA Authentication Profile 1.0", March 2017.|
|[RFC4211]||Schaad, J., "Internet X.509 Public Key Infrastructure Certificate Request Message Format (CRMF)", RFC 4211, DOI 10.17487/RFC4211, September 2005.|
|[RFC4226]||M'Raihi, D., Bellare, M., Hoornaert, F., Naccache, D. and O. Ranen, "HOTP: An HMAC-Based One-Time Password Algorithm", RFC 4226, DOI 10.17487/RFC4226, December 2005.|
|[RFC4949]||Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007.|
|[RFC6238]||M'Raihi, D., Machani, S., Pei, M. and J. Rydell, "TOTP: Time-Based One-Time Password Algorithm", RFC 6238, DOI 10.17487/RFC6238, May 2011.|
|[RFC6819]||Lodderstedt, T., McGloin, M. and P. Hunt, "OAuth 2.0 Threat Model and Security Considerations", RFC 6819, DOI 10.17487/RFC6819, January 2013.|
|[SMS]||3rd Generation Partnership Project, "Technical realization of the Short Message Service (SMS)", 3GPP Technical Specification (TS) 03.40 V7.5.0 (2001-12), January 2002.|
|[W3C.REC-geolocation-API-20161108]||Popescu, A., "Geolocation API Specification 2nd Edition", World Wide Web Consortium Recommendation REC-geolocation-API-20161108, November 2016.|
|[W3C.WD-webauthn-20170216]||Bharadwaj, V., Le Van Gong, H., Balfanz, D., Czeskis, A., Birgisson, A., Hodges, J., Jones, M., Lindemann, R. and J. Jones, "Web Authentication: An API for accessing Scoped Credentials", World Wide Web Consortium Working Draft WD-webauthn-20170216, February 2017.|
In some cases, the amr claim value returned may contain a single Authentication Method Reference value. For example, the following amr claim value indicates that the authentication performed used an iris scan biometric:
"amr": ["pwd", "kba"]
In other cases, the amr claim value returned may contain multiple Authentication Method Reference values. For example, the following amr claim value indicates that the authentication performed used a password and knowledge-based authentication:
Caleb Baker participated in specifying the original set of amr values. Jari Arkko, John Bradley, Ben Campbell, Brian Campbell, William Denniss, Linda Dunbar, Stephen Farrell, Paul Kyzivat, Elaine Newton, James Manger, Catherine Meadows, Alexey Melnikov, Kathleen Moriarty, Nat Sakimura, and Mike Schwartz provided reviews of the specification.
[[ to be removed by the RFC editor before publication as an RFC ]]