Merge branch '22450-restrict-origin' into 'master'

Set a restrictive CORS policy for the API

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/22450

See merge request !1998

config/application.rb

@@ -99,13 +99,24 @@ module Gitlab
     config.action_view.sanitized_allowed_protocols = %w(smb)
-    config.middleware.use Rack::Attack
+    config.middleware.insert_before Warden::Manager, Rack::Attack
     # Allow access to GitLab API from other domains
-    config.middleware.use Rack::Cors do
+    config.middleware.insert_before Warden::Manager, Rack::Cors do
+      allow do
+        origins Gitlab.config.gitlab.url
+        resource '/api/*',
+          credentials: true,
+          headers: :any,
+          methods: :any,
+          expose: ['Link']
+      end
+
+      # Cross-origin requests must not have the session cookie available
       allow do
         origins '*'
         resource '/api/*',
+          credentials: false,
           headers: :any,
           methods: :any,
           expose: ['Link']