implement openID authentication

app/controllers/users/omniauth_callbacks_controller.rb

@@ -0,0 +1,32 @@
+class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
+  skip_before_filter :verify_authenticity_token
+
+  [:novell, :google, :facebook, :twitter].each do |provider|
+    define_method(provider) { handle(provider) }
+  end
+
+  private
+    def handle(provider)
+
+      auth_hash = request.env['omniauth.auth']
+      openid = Openid.find_for_oauth(auth_hash) # Get or create openid
+      # If openid exists and is associated with a user, sign in with associated user,
+      # even if the email of the associated user and the email of the provided openid are different
+      unless user = openid.user
+        user = User.find_for_auth(auth_hash, current_user) # Get or create users
+      end
+
+      begin
+        user.save!
+        if openid.user != user
+          openid.user = user
+        end
+        openid.save!
+
+        sign_in user
+        redirect_to root_path, notice: user.email + " signed in successfully with #{provider}"
+      rescue Exception => e
+        redirect_back_or_to new_user_registration_path, alert: 'Failed' + e.message
+      end
+    end
+end