Modify local instead of global request

in apply_authentication_headers_for helper
to allow usage of different authenticated user in one testcase

spec/auth_helpers.rb

@@ -3,6 +3,6 @@
 module AuthHelpers
   def apply_authentication_headers_for(user)
     user_headers = user.create_new_auth_token
-    @request.headers.merge!(user_headers)
+    request.headers.merge!(user_headers)
   end
 end