GUACAMOLE-937: Return null on bindAs() failures. Rely on caller to interpret and handle failures.

Throwing GuacamoleInvalidCredentialsException breaks separation of
concerns (bindAs() shouldn't assume that it's being used during login
and that credentials given are the Guacamole user's credentials), and
has unintended side effects (throwing subclasses of
GuacamoleUnauthorizedException causes implicit session invalidation).
2 files changed