Merge branch 'kerberos_require' into '7-12-stable'

Kerberos require to stable 7.12

!819 to 7-12-stable

cc @jacobvosmaer

See merge request !827

config/initializers/7_omniauth.rb

@@ -17,3 +17,11 @@ OmniAuth.config.allowed_request_methods << :get if Gitlab.config.omniauth.auto_s
 OmniAuth.config.before_request_phase do |env|
   OmniAuth::RequestForgeryProtection.new(env).call
 end
+
+if Gitlab.config.omniauth.enabled
+  Gitlab.config.omniauth.providers.each do |provider|
+    if provider['name'] == 'kerberos'
+      require 'omniauth-kerberos'
+    end
+  end
+end