Add table to store omniauth details for users.

app/models/omniauth_user.rb

@@ -0,0 +1,5 @@
+class OmniauthUser < ActiveRecord::Base
+  belongs_to :user
+
+  validates :user, presence: true
+end

db/migrate/20170824183110_create_omniauth_users.rb

@@ -0,0 +1,12 @@
+class CreateOmniauthUsers < ActiveRecord::Migration
+  def change
+    create_table :omniauth_users do |t|
+      t.string :provider
+      t.string :uid
+      t.string :email
+      t.references :user, index: true, foreign_key: true
+
+      t.timestamps null: false
+    end
+  end
+end