Re: [OAUTH-WG] OAuth 2.0 Token Introspection in RFC7662 : Refresh token?

[David Waite <[e-mail]>]

On Mar 1, 2020, at 10:11 PM, Andrii Deinega <[e-mail]> wrote:
> 
> How would the authorization server know who actually uses the
> introspection endpoint assuming that a protected resource and a client
> application use the same credentials (client_id and client_secret)?

In the external context, you have a client accessing a protected resource with an access token. The client should treat the token as opaque, and RFC7662 makes no allowances for that client to introspect its tokens.

If you control both the client and protected resource, you may decide to short-cut and have them share credentials. However, the client logic still should never be introspecting the tokens.

The security considerations also say that you must prove the authentication of the protected resource, which I have interpreted to mean that access tokens used to authorize the call to the introspection endpoint must be issued to a confidential client - public clients cannot protect credentials to perform an authentication. You want to limit introspection to prevent denial of service and probing attacks, and to limit the amount of information on viable attacks conveyed if someone steals a token.

-DW

> 
> Regards,
> Andrii
> 
> On Sun, Mar 1, 2020 at 7:38 PM David Waite <[e-mail]> wrote:
>> 
>> I would expect the AS to invalidate the refresh token in this case, which would not require a refresh token mode nor necessarily any signaling back to the resource.
>> 
>> -DW
>> 
>>> On Mar 1, 2020, at 12:12 AM, Andrii Deinega <[e-mail]> wrote:
>>> 
>>> Hello Bill,
>>> 
>>> I'm just thinking out loud about possible scenarios for a protected
>>> resource here... It may decide to revoke a refresh token if a client
>>> application tried to use it instead of an access token when the
>>> protected resource is paranoid about security. In order to do that an
>>> introspection response should include a non-standard parameter which
>>> indicates that the requested token is refresh_token.
>>> 
>>> A user of the introspection endpoint should rely only on a value of
>>> the active parameter (which is a boolean indicator) of the endpoint
>>> response. This applies to both types of tokens. Note, the expiration
>>> date, as well as other parameters, are defined as optional in the
>>> specification. Both token types can be revoked before the expiration
>>> date comes even if this parameter is presented as part of the
>>> response. In my opinion, there are a number of reasons why this check
>>> (for a refresh token) can be useful on the client application side.
>>> 
>>> --
>>> Regards,
>>> Andrii
>>> 
>>> 
>>> On Fri, Feb 28, 2020 at 1:59 AM Bill Jung
>>> <bjung=[e-mail]> wrote:
>>>> 
>>>> Hello, hopefully I am using the right email address.
>>>> 
>>>> Simply put, can this spec be enhanced to clarify "Who can use the introspection endpoint for a refresh token? A resource provider or a client app or both?"
>>>> 
>>>> RFC7662 clearly mentions that the user of introspection endpoint is a 'protected resource' and that makes sense for an access token. If we allow this to client apps, it'll give unnecessary token information to them.
>>>> However, the spec also mentions that refresh tokens can also be used against the endpoint.
>>>> In case of refresh tokens, user of the endpoint should be a client app because refresh tokens are used by clients to get another access token. (Cannot imagine how/why a resource server would introspect a refresh token)
>>>> 
>>>> Is it correct to assume that the endpoint should be allowed to client apps if they want to examine refresh token's expiry time? Then the RFC should clearly mention it.
>>>> 
>>>> Thanks in advance.
>>>> 
>>>> <Details from the spec>
>>>> In https://tools.ietf.org/html/rfc7662
>>>> In '1.  Introduction' section says,
>>>> "This specification defines a protocol that allows authorized
>>>> protected resources to query the authorization server to determine
>>>> the set of metadata for a given token that was presented to them by
>>>> an OAuth 2.0 client."
>>>> Above makes clear that user of the endpoint is a "protected resource".
>>>> 
>>>> And under 'token' in '2.1.  Introspection Request' section says,
>>>> "For refresh tokens,
>>>> this is the "refresh_token" value returned from the token endpoint
>>>> as defined in OAuth 2.0 [RFC6749], Section 5.1."
>>>> So looks like a refresh token is allowed for this endpoint.
>>>> 
>>>> 
>>>> Bill Jung
>>>> Manager, Response Engineering
>>>> [e-mail]
>>>> w: +1 604.697.7037
>>>> Connect with us:
>>>> 
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