<div dir="ltr"><div class="gmail_default" style="font-family:trebuchet ms,sans-serif">Yep this is a good question.</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif"><br></div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif">From memory the idea of the client notification token was to protect the notification endpoint for what we now call "Push" mode. </div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif">I think the concept was to not overload the auth_req_id to be both an identifier and a "bearer token" and I suppose to give a bit of extra security in case the auth_req_id leaked. Given that the Client generates the client_notification_token I suppose it gives a bit more architectural flexibility - i.e. the Client could protect its notification endpoint in a similar manner to other endpoints that it has, perhaps rejecting requests with a bad client notification token at an API gateway level before the request even reaches the application logic that would look up the auth_req_id. </div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif"><br></div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif">However I tend to agree that it is now redundant. Poll mode doesn't really need such a token, and in Push mode we've tightened up the spec such that the ID Token is a detached signature that the Client must verify. I'll open an issue in the tracker so we can discuss on the next call.</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif"><br></div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif">Dave</div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif"><br></div><div class="gmail_default" style="font-family:trebuchet ms,sans-serif"><br></div></div><br><div class="gmail_quote"><div dir="ltr">On Mon, 31 Dec 2018 at 16:24, Brian Campbell via Openid-specs-mobile-profile <<a href="mailto:openid-specs-mobile-profile@lists.openid.net" target="_blank">openid-specs-mobile-profile@lists.openid.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Eric raises a good question here that I don't have an immediate answer for. Honestly, I hadn't really thought critically about the purpose of the <font face="arial, helvetica, sans-serif">client_notification_token relative to what the <font face="arial, helvetica, sans-serif">auth_req_id provides. Perhaps someone who was involved when the <font face="arial, helvetica, sans-serif">client_notification_token concept was introduced can shed some light on the motivations behind it and if there's reason for it beyond what's mentioned here? </font></font></font></div><br><div class="gmail_quote"><div dir="ltr">On Mon, Dec 31, 2018 at 6:07 AM Eric Fazendin via Openid-specs-mobile-profile <<a href="mailto:openid-specs-mobile-profile@lists.openid.net" target="_blank">openid-specs-mobile-profile@lists.openid.net</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div class="gmail_default"><div class="gmail_default"><font face="arial, helvetica, sans-serif">auth_req_id and client_notification_token seem redundant. Unless we can clarify why both are necessary, I suggest we remove client_notification_token from the spec.</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">Based on 7.1, it's described as "It is a bearer token provided by the Client that will be used by the OpenID Provider to authenticate the callback request to the Client."</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">10.2 and 10.3.1 says, "The Client MUST verify the client_notification_token used to authenticate the request is valid and is associated with the auth_req_id received in the Ping callback."</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">There is no further elaboration of why it's needed or what additional value it might provide the client. Examples suggest it is in a GUID format. Perhaps it could be a JWT and therefore reduce the state required to manage by the client, but it's not cryptographically bound to the auth_req_id, so the client is going to have to track the state of a given client_notification_token as being associated to a given auth_req_id.</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">auth_req_id is described in 7.3 as "This is a unique identifier to identify the authentication request made by the Client."</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">7.4 says, "The Client MUST keep the auth_req_id in order to validate the callbacks received in Ping and Push modes or to use when making a token request in Poll and Ping modes."</font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif"><br></font></div><div class="gmail_default"><font face="arial, helvetica, sans-serif">I don't understand the value of the client_notification_token when there is also the auth_req_id. The client_notification_token adds unnecessary complexity to client implementations. If the client wants to track authentication requests and associate them to Ping and Push Callbacks, they can do so with only the auth_req_id.</font></div></div></div></div>
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