Added "devise" for authentication.

app/models/user.rb

@@ -1,2 +1,12 @@
 class User < ActiveRecord::Base
+  # Include default devise modules. Others available are:
+  # :confirmable, :lockable, :timeoutable and :omniauthable
+  devise :database_authenticatable,
+    # :registerable,
+    # :recoverable,
+    # :rememberable,
+    :trackable,
+    :validatable,
+    :timeoutable,
+    :lockable
 end