Use user from request context

[prudloff-insite]

This fixes #758 for us but it might not be the correct solution.

I find it a bit strange that Parser::getUserIdentity() does not check if Parser::getOptions() returns null before trying to use its result. (The documentation of Parser::getOptions() acknowledges that it can return null.)

[JeroenDeDauw]

I'm not sure either that your change is correct. It seems safer to get the user from the Parser object rather than via a global.