Possible bypass of token claim validation when OAuth2 Introspection caching is enabled

ORY Oathkeeper is an Identity & Access Proxy (IAP) and Access Control Decision API that authorizes HTTP requests based on sets of Access Rules. When you make a request to an endpoint that requires the scope foo using an access token granted with that foo scope, introspection will be valid and that token will be cached. The problem comes when a second requests to an endpoint that requires the scope bar is made before the cache has expired. Whether the token is granted or not to the bar scope, introspection will be valid. A patch will be released with v0.38.12-beta.1. Per default, caching is disabled for the oauth2_introspection authenticator. When caching is disabled, this vulnerability does not exist. The cache is checked in `func (a *AuthenticatorOAuth2Introspection) Authenticate(...)`. From `tokenFromCache()` it seems that it only validates the token expiration date, but ignores whether the token has or not the proper scopes. The vulnerability was introduced in PR #424. During review, we failed to require appropriate test coverage by the submitter which is the primary reason that the vulnerability passed the review process.