The idea is not totally clear. But you may be looking for something like social login, or what we call inbound identity:
In your scenario outlined above, I think you're basically saying you want users from gluu1 to be able to access web 2 via their gluu1 authentication server.
So the user would navigate to web2, there would be some mechanism to determine the user has an account in gluu1 (what we call "Discovery"), the user would get redirected to gluu1 for login, and then redirected back to web2 with a session.
If that's the idea, you will want to follow the guide above.