Returns an Authorization from basic credentials.
This method must either return a Future
that yields an Authorization or return null.
If this method returns null, the invoking Authorizer will disallow further
request handling and immediately return a 401 status code. If this method returns an
Authorization, it will be set as the Request.authorization and request handling
will continue to the Authorizer.nextController.
Source
Future<Authorization> fromBasicCredentials( AuthBasicCredentials usernameAndPassword);