OAuth 2.0 Web Message Response Mode

This specification defines a new response mode for RFC6749 that uses HTML5 Web Messaging (a.k.a window.postMessage()) instead of the redirect for the Authorization Response from the Authorization Endpoint. This specification provides two modes Simple mode returns the Authorization Response directly to the client web page. Relay mode does not return the Authorization Response directly to the client web page but returns it to a child frame created by the client web page via the client web page.

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.

For the purposes of this specification, the following terms and definitions apply.

window object that the client created

A window object in the iframe created by the Main Window() or its child iframe. It is used to relay the Authorization Request from the client to the Authorization Server. The request is expected to have prompt=none defined in OpenID Connect Core. It is expected to be used when the End User is in the "authenticated" state at the Authorization Server so that prompt=none succeeds. Authorization Server SHOULD NOT send Set-Cookie header in the response.

A popup window object created by the Main Window(), via window.open(), to send the Authorization Request to the Authorization Endpoint. It is used when the user is not in the Authenticated state on the Authorization Server or the client has not received the authorization yet.

A window object in the iframe created by the Main Window() that receives Authorization Response in Relay Mode ().

Authorization

As stated above, this response mode provides two modes.

In the Simple mode, the protocol flows as follows.

The authorization request and response sequence when using Authenticated Window will be like this.

+----------> | | Main | |Authenticated | |Authorization | | Window | |Window | |Endpoint | | <-----------+ <----------+ | +--------+ 3.Send +---------------+ 3.Authz +--------------+ web message Response as Authz via JavaScript code Response ]]> Below is the description of the each steps in the above sequence diagram. Main Window creates the Unauthenticated Windows as an iframe to send Authorization Request and sets the URI of the Authorization Request as the src value of the iframe. The Authorization Request that is specified by the src value of the iframe of the Unauthenticated Window, which was set by the Main Window, is sent to Authorization Endpoint. Authorization Server determines if the End User is logged in state and checks if it can return the Authorization Response without interacting with the User. If it determines that it can, it will render the HTML5 that includes the JavaScript code that sends the Authorization Response. The Authorization Response is passed to the Main Window from the Unauthenticated Window using Web Message through the JavaScript.

When using Unauthenticated Window, the Authorization sequence would be as follows:

+----------> +-----+ | Main | |Unauthenticated| |Authorization | |3.User | Window | |Window | |Endpoint | |Interaction | <-----------+ <----------+ <-----+ +--------+ 5.Send +---------------+ 4.Authz +--------------+ web message Response as Authz via JavaScript code Response ]]> It is almost identical to the sequence that used Authenticated Window except: The way the window object that is used to send the Authorization Request is different. i.e., iframe v.s. window.open(). End User may interact with the Authorization Server before the Authorization Response is being sent. The relationship of the window that accesses the Authorization Endpoint and the Main Window is different. i.e., window.parent v.s. window.opener.

The protocol flow of the Relay mode will be as follows.

The authorization sequence that uses Unauthenticated Window will be:

Message Target Window <-------+ | | | | | +-----------------------+ 7.Send web message as 1.Create iframe Authz Response | | +--+-----+ 2.Create iframe +--------+-----+ +---------+ | +----------------------> Un- +---------> | | Main | | Authenticated| 3.Authz | Authz | | Window <----------------------+ Window | Request | Endpoint| | | 5.Send web message | | | | +------+-+ as Relay Request +--^-------^---+ +---+-----+ | | | | +---------------------------+ +-----------------+ 6.Relay Response 4.Authz Response by Javascript code ]]> Create iframe (Message Target Window) through Main Window. It will receive the Authorization Response. Create iframe (Unautenticated Window) through Main Window. The Authorization Request URI is set as the src value of the iframe. This iframe is used to send the Authorization Request. Authorization Request specified in the src value by the Main Window is sent to the Authorization Endpoint. Authorization Server checks the login status of the End User and whether it can return the Authorization Response without the End User interaction. If it is, then it will render the HTML5 that includes JavaScript code that sends Relay Request and Authorization Response. Unauthenticated Window sends Relay Request as a Web Message to the Main Window throught the JavaScript code. Main Window returns the Relay Response. Unauthenticated window obtains the window object of the Message Target Window via the MessageEvent object in the Relay Response and send Authorization Response as a Web Message.

The authorization sequence that uses the Authenticated Window follows almost the same sequence.

Message Target Window <-------+ | | | | | +-----------------------+ 7.Send web message as 1.window.open() Authz Response | | +--+-----+ 2.Create iframe +--------+-----+ +---------+ | +----------------------> Un- +---------> +---+ | Main | | authenticated| 3.Authz | Authz | |3.User | Window <----------------------+ Window | Request | Endpoint| |Interaction | | 5.Send web message | | | <---+ +------+-+ as Relay Request +--^-------^---+ +---+-----+ | | | | +---------------------------+ +-----------------+ 6.Relay Response 4.Authz Response by Javascript code ]]> The differences are, just like in the Simple Mode: The way the window object that is used to send the Authorization Request is different. i.e., iframe v.s. window.open(). End User may interact with the Authorization Server before the Authorization Response is being sent. The relationship of the window that accesses the Authorization Endpoint and the Main Window is different. i.e., window.parent v.s. window.opener.

Web Messaging Response Mode defines the following Authorization Request parameters. REQUIRED. ASCII string "web_message". REQUIRED. The origin URI of the URI of the Main Window. If web_message_uri is not specified, Authorization Responsewill be sent to the origin specifed by the redirect_uri. OPTIONAL. The origin URI that Message Target Window references. When it is specified, Authorization Response will not be returned to the redirect_uri but Relay Request/Responses are used. OPTIONAL or REQUIRED. The DOM id value that points to the Message Target Window. REQUIRED if web_message_uri is used. Authorization Response obtains the window object of Message Target Window via Relay Request/Relay Response with the Main Window. If it is not specified, Authorization Responsewill be sent to the calling window. Main WIndow creates an event listener before sending the Authorization Request, and sends Authorization Request that uses these parameters to either Authenticated Window or Unauthenticated Window. The following example depicts the Authorization Request to the Unauthenticated Window in the Simple Mode.

Actual authorization request will look like:

Following depicts the Authorization Request to Authenticated Window in Relay Mode.

Actual authorization request will look like:

Message Target Window in Relay mode creates an event listener to receive Authorization Response.

Web Messages between Authenticated Window or Unauthenticated Window and Main Window or Message Target Window takes the following fields. field type required description type string true prepare_authorization_response OR authorization_response response object false used when type=authorization_response Type attribute values are described in the following table. mode sender receiver type description Simple Mode Authenticated Window or Unauthenticated Window Main Window authorization_response response including Authorization Response Relay Mode Authenticated Window or Unauthenticated Window Main Window relay_request Request to get the reference to the window object of the Main Window Relay Mode Main Window Authenticated Window or Unauthenticated Window relay_response The response to the relay_request Relay Mode Authenticated Window or Unauthenticated Window Message Target Window authorization_response Response that includes Authorization Response

Authorization Server needs to render the JavaScript code to return the Authorization Response when response_mode was web_message at the time of Authorization Request at Authorization Endpoint. Authorization Server MUST verify the following before returning Authorization Response. The origin specified by redirect_uri is white-listed. The origin specified by web_message_uri is white-listed. If verified, it MUST return the response including the JavaScript code such as:

Authorization Response ]]> If web_message_uri and web_message_target request parameters are specified in Authorization Request, window object sent by postMessage() is not to be set to window.opener or window.parent but to a specific frame, responses such as follows should be returned.

Authorization Response ]]>

The following field is added to RFC7519. field type description web_message_uris array List of origins that are allowed as web_message_uri in the Authorization Request.

Followings are added to OAuth Dynamic Client Registration Metadata Registry. Client Metadata Name: "web_message_uris" Client Metadata Description: List of origins that are allowed as web_message_uri in the Authorization Request. Change Controller: IESG Specification Document(s): This document

In addition to the all the security considerations discussed in OAuth 2.0, the following security considerations SHOULD be taken into account.

Follwoing people contributed to the creation of this document .

-01 Updated authors contacts -00 Initial Draft.