Add prompt=none authorization param handler

[batalla3692]

In order to handle SSO authentication, we must perform silent authentication. To do that, the docs point to add a prompt=none to the authorization path.

There is no way to do that dinamically. I can perform silent authentication If I add this to initializers/auth0.rb:

authorize_params: {
	scope: 'openid',
	prompt: 'none'
}

But this will try to perform silent authentication always, and if the user is not logged in then a redirection to the failure callback will be fire.

I need a way to add the prompt param dinamically, so if a user is not logged in I can redirect him to the Auth0 login page. Is that possible?

[batalla3692]

I create a pull request #59 to add this functionality.