A few users informed us that they were seeing “403 Forbidden: The server understood the request, but is refusing to fulfill it.” while trying to login. My friend too has been seeing this from the last hour or two while trying to login to our website via twitter.
In my friends case this is only happening when he’s accessing the site through mobile.
The error occurs after the user has entered their credentials on twitter. The user is never redirected back to our site and instead is shown this 403 error.