[Openid-specs-ab] OpenID Connect Logout using HTTP GET

Justin Richer jricher at mit.edu
Tue Feb 17 12:42:25 UTC 2015


In my mind, the RP should never be generating an ID token. For logout 
(or other id_token_hint uses), the RP should pass along the ID token 
that it received from its last login event, even if it's expired. It's 
essentially a "session key", tying the two actions together. The IdP can 
validate the token even if it's dead already (check issuer, signatures, 
etc) and make sense of it in context of the requested action.

  -- Justin

On 2/17/2015 4:51 AM, Thomas Broyer wrote:
> One issue with this scheme is that this is typically implemented as 
> web page with <img> elements and a <meta refresh> to redirect to some 
> other place after all images have loaded, but empty/blank in all other 
> aspects. That means that an misbehaving RP could impair the UX of the 
> whole "platform" (and more specifically the OP) if it doesn't respond 
> in a timely manner. Because there's no way to indicate timeouts in 
> HTML, the only way to workaround this is to add JavaScript (setTimer 
> in DOMContentLoaded, to trigger redirection before onload if that ones 
> takes too much time, possibly cancelled in onunload if onload comes 
> fast enough –shouldn't technically be needed, but not all browsers 
> behave the same IIRC); and/or to add a message with a link to be 
> clicked "if logging out takes too much time".
>
> Otherwise OK with the proposal overall. My notes below:
>
> I don't quite understand why it talks about the end_session_endpoint 
> and post_logout_redirect_uris; it should just defer to RP-Initiated 
> Logout, saying it extends it (so it must indeed be supported by the OP).
>
> In “OP Logout Functionality”, “register this related metadata value” 
> should probably be “advertize this related metadata value”.
>
> What claims should be included in the id_token? What does the "exp" 
> claim would stand for? IIUC, the "exp" claim for the ID Token 
> initially returned during authentication represents the authentication 
> expiration [1], but the logout_uri is called after the authentication 
> has been revoked or has expired here, so the "exp" claim cannot have 
> that meaning in this specific case. Should the id_token here be 
> generated specifically for this call, with a very short expiration? or 
> should/could it be the same as the one last sent to the RP during 
> authentication? How should the RP validate it? (because it's not 
> “received via direct communication between the Client and the Token 
> Endpoint”, I suppose the RP MUST validate the signature?)
>
> [1] This, to begin with, is really not clear at all; it's only said 
> once “in passing” in 
> <https://openid.net/specs/openid-connect-core-1_0.html#Authentication> 
> without even mentioning the "exp" claim explicitly (“The 
> Authentication result is returned in an ID Token, as defined in 
> Section 2. It has Claims expressing such information as the Issuer, 
> the Subject Identifier, when the authentication expires, etc.”; and 
> note that this section, and thus this sentence, is absent from 
> openid-connect-basic-1_0 for instance.) The "exp" claim is always 
> defined as the “expiration time on or after which the ID Token MUST 
> NOT be accepted for processing”, which is reflected in the “ID Token 
> Validation” section 
> <https://openid.net/specs/openid-connect-core-1_0.html#IDTokenValidation>, 
> but that one only applies to validating the id_token received during 
> authentication, not how the OP should validate id_token_hint at the 
> authorization endpoint or end_session_endpoint, or the id_token at the 
> logout_uri here. FWIW, I had originally understood that as that the ID 
> Token could have a validity timeframe of a few minutes only, and 
> that's how I implemented it! And the examples using an ID Token with a 
> validity timeframe of 1000 seconds (approx. 15 minutes) don't help in 
> the understanding. It's never said either how an RP should behave 
> should the ID Token expire: should it re-authenticate (possibly using 
> prompt=none and id_token_hint –note that the ID Token could have 
> expired here, so having a definition of how the OP should validate it 
> would be great) to check the user is still authenticated at the OP and 
> possibly get a new ID Token?
>
> On Tue Feb 17 2015 at 03:45:31 Mike Jones <Michael.Jones at microsoft.com 
> <mailto:Michael.Jones at microsoft.com>> wrote:
>
>     An updated version is attached.  Changes were:
>
>     16-Feb-15            Added an optional id_token parameter to the
>     logout_uri to authenticate requests and differentiate between
>     sessions, plus related metadata values.  Added that non-200 HTTP
>     status codes can be used when the logout fails.  Clarified when
>     post-logout redirection to an RP occurs.
>
>     I believe that this addresses the comments received to date.
>
>     -- Mike
>
>     -----Original Message-----
>     From: Openid-specs-ab
>     [mailto:openid-specs-ab-bounces at lists.openid.net
>     <mailto:openid-specs-ab-bounces at lists.openid.net>] On Behalf Of
>     Mike Jones
>     Sent: Sunday, February 15, 2015 11:03 PM
>     To: John Bradley; Torsten Lodderstedt
>     Cc: openid-specs-ab at lists.openid.net
>     <mailto:openid-specs-ab at lists.openid.net>
>     Subject: Re: [Openid-specs-ab] OpenID Connect Logout using HTTP GET
>
>     I'm increasingly thinking that we should allow the OP to include
>     the ID Token for the RP as a query parameter in the logout
>     request.  I'm thinking this for two reasons:
>
>     1.  It would validate to the RP that the logout request is legitimate.
>
>     2.  It would tell the RP which session to log out, should multiple
>     users be logged in at the RP from the OP.
>
>     I don't think we should make including the ID Token required,
>     since deployment circumstances will differ. In some cases, the
>     extra validation is important.  In others, it isn't.
>
>     If we do this, in the Discovery and Recovery metadata, we should
>     have the RP and the OP say whether the require and provide the ID
>     Token value as part of the logout message to the RP.
>
>     -- Mike
>
>     -----Original Message-----
>
>     From: John Bradley [mailto:ve7jtb at ve7jtb.com]
>
>     Sent: Sunday, February 15, 2015 11:34 AM
>
>     To: Torsten Lodderstedt
>
>     Cc: Thomas Broyer; Mike Jones; openid-specs-ab at lists.openid.net
>     <mailto:openid-specs-ab at lists.openid.net>
>
>     Subject: Re: [Openid-specs-ab] OpenID Connect Logout using HTTP GET
>
>     Both
>
>     forcing a user to logout of a RP might also be used as part of a
>     larger phishing attack, especially if the IdP returns the user to
>     the bad guys landing page by redirecting to the
>     post_logout_redirect_uri.
>
>     That redirect URI needs to be registered but without
>     authenticating the RP via having a id_token for the user Bad RP A
>     could log the user out of all sessions and redirect the user to
>     itself, without the user currently being logged in.
>
>     Without the id_token all the IdP can do is log the user out of all
>     sessions.
>
>     Though when we start talking about IdP session management things
>     get a bit fuzzy,  Many IdP will automatically log the user back in
>     to a RP if they are still logged in to the IdP, the IdP may not
>     have any real notion of state per RP connection.
>
>     John B.
>
>     On Feb 15, 2015, at 1:29 PM, Torsten Lodderstedt
>     <torsten at lodderstedt.net <mailto:torsten at lodderstedt.net>> wrote:
>
>     >
>
>     >
>
>     > against the RP or the user?
>
>     >
>
>     > Am 15.02.2015 um 17:22 schrieb John Bradley:
>
>     >> It might be used as a denial of service via xsrf.
>
>     >
>
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