Re: [OAUTH-WG] Quick question about error response for "response_type=unknown"

[John Bradley <[e-mail]>]

If the Authorization server, doesn't understand the response_type and has no other way to determine what sort of flow the client is expecting, I don't see any choice other than returning a error to the user/browser.

In the case of an unknown response_type the client could also be expecting postMessage, or making a direct connection.  You just don't know.

There may be cases that the Authorization server could infer how to reply based on the client_id, if the client perhaps doesn't have a client secret issued to it, you could guess that it is using a fragment encoded flow.

I however don't know that guessing is a good practice.   Probably best to always return an error response without a redirect.

John B.
On 2012-02-21, at 8:34 AM, matake@gmail wrote:

> So the answer is "Show the error to the user without redirecting back to the client", right?
> I'm now developing OAuth2 and OpenID Connect ruby library, and both of them return errors
> 
> case 1. redirect with error in query if response_type is "code" but it's not supported
> case 2. redirect with error in fragment if response_type is "token code", "token id_token", "token code id_token" or "code id_token" but it's not supported
> case 3. otherwise show error to the user without redirect since server cannot understand the response_type at all
> 
> But other server might not understand some of response_types listed in case 2 at all and choose case 3 in such case.
> (ie. OAuth servers which don't understand OpenID Connect won't understand "id_token")
> 
> So I'm afraid that it reduces interoperability, a bit.
> 
> On 2012/02/21, at 13:22, William Mills wrote:
> 
>> I does allow some parts of your server config to be discovered.  More of a problem in error responses is usually echoing back the user data, or allowing user enumeration for example.  Care is required, but you don't have a ton of options here.
>> 
>> From: Igor Faynberg <[e-mail]>
>> To: [e-mail] 
>> Sent: Monday, February 20, 2012 9:37 AM
>> Subject: Re: [OAUTH-WG] Quick question about error response for "response_type=unknown"
>> 
>> Could there be a potential security hole in providing an error response?  (Not that I see it, but many problems in the past had been caused by helpful responese.)
>> 
>> Igor
>> 
>> On 2/20/2012 11:57 AM, William Mills wrote:
>>> 
>>> Respond with an error in protocol.  Thta won't include a redirect, and the client has to know what to do.
>>> 
>>> From: nov matake <[e-mail]>
>>> To: oauth WG <[e-mail]> 
>>> Sent: Monday, February 20, 2012 6:11 AM
>>> Subject: [OAUTH-WG] Quick question about error response for "response_type=unknown"
>>> 
>>> Hi OAuthers,
>>> 
>>> My apologies if you already discussed this.
>>> 
>>> When OAuth server received unknown response_type, how should the server handle the error?
>>> 
>>> 1. Show the error to the user without redirecting back to the client
>>> 2. Redirect back to the client including the error in query
>>> 3. Redirect back to the client including the error in fragment
>>> 
>>> Since choosing 2 or 3 is impossible in this case, 1 seems reasonable for me.
>>> 
>>> 
>>> --
>>> nov
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