implement openID authentication

app/models/openid.rb

@@ -0,0 +1,22 @@
+class Openid < ActiveRecord::Base
+  belongs_to :user
+  validates :provider, :uid, :presence => true
+
+  # Searches for openid based on provider and uid.
+  # Returns found openid or a new openid.
+  # ====Returns
+  # * Openid::ActiveRecord_Relation -> openid
+  def self.find_for_oauth(auth)
+    openid = Openid.where(provider: auth.provider, uid: auth.uid).first_or_initialize
+
+    if openid.new_record?
+      openid.email = auth.info.email
+      if existing_openid = Openid.where(email: openid.email).first
+        openid.user_id = existing_openid.user_id
+      end
+    end
+    openid
+
+  end
+
+end