Demo authentication should enforce a username

[pmeier]

There is no check for that. Worse, if running without a central password, not putting anything for username and password actually authenticates. Reported in #156 (reply in thread).

[pmeier]

On second thought, maybe this is actually a good thing? Like, if users don't configure anything they are still hit by the authentication screen. Being able to just click "Login" without filling in anything, could count as feature?

[pmeier]

On third thought, I agree with my initial statement. As proposed in #179, the dummy authentication should not be the default and thus it is ok to require a username being supplied.