OAuth 2.0 Authorization Server Issuer Identifier in Authorization Response
draft-meyerzuselhausen-oauth-iss-auth-resp-00

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Web Authorization Protocol                         K. Meyer zu Selhausen
Internet-Draft                                                 Hackmanit
Intended status: Standards Track                                 D. Fett
Expires: 29 April 2021                                           yes.com
                                                         26 October 2020

   OAuth 2.0 Authorization Server Issuer Identifier in Authorization
                                Response
             draft-meyerzuselhausen-oauth-iss-auth-resp-00

Abstract

   This document specifies a new parameter "iss" that is used to
   explicitly include the issuer identifier of the authorization server
   in the authorization response of an OAuth authorization grant.  If
   implemented correctly, the "iss" parameter serves as an effective
   countermeasure to "mix-up" attacks.

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 29 April 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions and Terminology . . . . . . . . . . . . . . .   3
   2.  Response Parameter "iss"  . . . . . . . . . . . . . . . . . .   3
     2.1.  Example Authorization Response  . . . . . . . . . . . . .   4
     2.2.  Providing the Issuer Identifier "iss" . . . . . . . . . .   4
     2.3.  Validation of the Issuer Identifier "iss" . . . . . . . .   5
   3.  Authorization Server Metadata . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  OAuth Authorization Server Metadata . . . . . . . . . . .   7
     5.2.  OAuth Parameters Registration . . . . . . . . . . . . . .   7
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   The OAuth authorization framework [RFC6749] allows clients to
   interact with multiple independent authorization servers under the
   control of separate entities.  Some OAuth grant types utilize the
   resource owner's user-agent to deliver the authorization server's
   response to the OAuth client.  One example of this pattern is the
   authorization response of the authorization code grant.

   The authorization response as specified in Section 4.1.2. of
   [RFC6479] does not contain any information about the identity of the
   authorization server which issued the response.  Therefore, clients
   receiving a response from the resource owner's user-agent cannot be
   sure who initially issued the response.  The lack of certainty about
   the origin of the response benefits a class of attacks called "mix-up
   attacks".

   This type of attack is a threat to all OAuth clients that interact
   with multiple authorization servers when at least one of these
   authorization servers is under an attacker's control.  There are

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   multiple ways in which an attacker can gain control over an
   authorization server supported by the client: For example, an
   authorization server could become compromised, or the attacker could