Disable external auths by default. Don't change settings for existing sites.

db/migrate/20140604145431_disable_external_auths_by_default.rb

@@ -0,0 +1,24 @@
+class DisableExternalAuthsByDefault < ActiveRecord::Migration
+
+  def enable_setting_if_default(name)
+    result = User.exec_sql("SELECT count(*) count FROM site_settings WHERE name = '#{name}'")
+    if result[0]['count'].to_i == 0
+      execute "INSERT INTO site_settings (name, data_type, value, created_at, updated_at) VALUES ('#{name}', 5, 't', now(), now())"
+    end
+  end
+
+  def up
+    users_count_query = User.exec_sql("SELECT count(*) FROM users")
+    if users_count_query[0]['count'].to_i > 1
+      # existing site, so keep settings as they are
+      enable_setting_if_default 'enable_yahoo_logins'
+      enable_setting_if_default 'enable_google_oauth2_logins'
+      enable_setting_if_default 'enable_twitter_logins'
+      enable_setting_if_default 'enable_facebook_logins'
+    end
+  end
+
+  def down
+    # No need to undo
+  end
+end