omniauth_controller for multiple providers.

omniauth_callbacks_controller.rb

class OmniauthCallbacksController < Devise::OmniauthCallbacksController

  def all
    #raise request.env["omniauth.auth"].to_yaml
    omniauth = request.env["omniauth.auth"]
    provider = User.from_omniauth(omniauth)
    if provider.persisted?
      flash.notice = "Successful login"
      sign_in(provider.user)
      @after_sign_in_url = after_sign_in_path_for(provider.user)
    else # If user has a validation error
      session["devise.user_attributes"] = user.attributes
      redirect_to new_user_registration_url
    end
  end

  alias_method :facebook, :all
end