@Override
    public URI getLoginURI() throws GuacamoleException {
        throw new GuacamoleResourceNotFoundException("No such resource.");
    }
Processes the given credentials, returning the identity represented by
the auth session token present in that request associated with the 
credentials. If no such token is present, or the token does not represent
a valid identity, null is returned.

@param credentials
    The credentials to extract the auth session token from.

@return
    The identity represented by the auth session token in the request,
    or null if there is no such token or the token does not represent a
    valid identity.
extensions/guacamole-auth-sso/modules/guacamole-auth-sso-ssl/src/main/java/org/apache/guacamole/auth/ssl/AuthenticationProviderService.java