Hi,

I just got a "Failed to introspect token" result when trying to use this new endpoint.
When I tried to find out what went wrong I observed that also no additional log entry was available.
Looking at the code (1.8.0.Final) of class TokenIntrospectionEndpoint revealed that in method
introspect() there is a try-catch that swallows all caught exception information.

In methods
   private AccessToken toAccessToken(String tokenString)
   private void authorizeClient()
its the same pattern.
A new exception gets thrown without any information about the caught exception.

You might consider opening an issue to add either some log statements in all catch blocks of this class
or propagate the exception information in the new thrown exceptions.

So currently there is no chance to find out why an introspection request failed.

Cheers,
  Manfred