Add HTTP Basic Authentication

[VasylShevchenko]

No description provided.

[dblock]

I'd expect username/password to be nil by default and blank being a valid value, at least for the password.

This needs tests and CHANGELOG entry.

[dblock]

I am not sure we want this. There's many ways to do auth and you can do basic auth outside of this controller when mounting it into an existing Rails application, no?