Allow other provider than email when logins

[MaicolBen]

Resolves #893
Resolves #859

I am not sure about adding a method overridable in the controller, maybe it should be a constant in user.

[lynndylanhurley]

Thanks @MaicolBen!!

[codeundercoverdev]

Where actually is the answer to this question? I have been getting redirected from github issue to github issue saying the answer is somewhere but all I see is a list of github issues refering the problem with zero code written anywhere?

[SanketKarve]

You need to override the provider method in session controller. This works for me:

def provider
  super
  'custom-provider-name'
end