Example 1: The user has validated first factor when accessing a service
protected by basic auth. When he tries to access another service protected
by second factor, he is redirected to second factor step to complete
authentication.
Example 2: The user has already validated second factor. When he access auth
service, he is redirected either to /loggedin page that displays an "already
logged in" page or to the URL provided in the "redirect" query parameter.
One can now customize the default authentication method for all sub-domains,
i.e., either 'two_factor' or 'basic_auth' and define specific authentication
method per sub-domain.
For example, one can specify that every sub-domain must be authenticated with
two factor except one sub-domain that must be authenticated with basic auth.
