I have a website with facebook login.
It has been stable and working for months.
No code change has happened for weeks.
Then, suddenly, the facebook login gives an error message:
Error
Given URL is not allowed by the Application configuration.: One or more of the given URLs is not allowed by the App's settings. It must match the Website URL or Canvas URL, or the domain must be a subdomain of one of the App's domains.
After debugging "for awhile", I reset my facebook app secret and it started to work again!