Allow Matrix Puppeting from other homeservers (or clarify error status if not possible)

[ShadowJonathan]

I noticed this while looking through the code for puppeting, it seems that the puppet is trying to send the access token to the same server the application service is currently connected to, is it (simply) possible for the puppeting mechanic to recognise when the access token is not pointing to the currently-connected server, and readjust accordingly?

Or is puppeting through an access token a feature which is granted from the status of Application Service? Does that mean that puppeting through other matrix homeservers will never work? If so, can the error message of "Failed to verify access token." be changed to "Cannot puppet users from another homeserver" when login-matrix is invoked?

[ShadowJonathan]

Moved to mautrix/python#25