An AuthenticationView is an interface that defines how a user can connect
with Gluon Cloud, by using one of the available login methods that are
defined in the application. Implementations will usually show up a list of
buttons that each represent one of these login methods. When a login method
is clicked, it could show a web page that starts the connect flow by loading
the login method's connect URL.
This method is called every time a request to Gluon Cloud is made that
requires an authenticated user and no authenticated user is currently
active in the application. Most probably, an implementation will show up
an authentication view that offers the user a way to connect to Gluon
Cloud using one of the available login methods. When the user finished
connecting, the provided contentConsumer will be called with
a JSON string that represents the connected user.
contentConsumer - a Consumer that is called when authentication