Tip: If it says "we're having trouble processing your login", that's due to a bug in Apple's SSO; refresh your expired developer.apple.com login cookie at that

Tip: If it says "we're having trouble processing your login", that's due to a bug in Apple's SSO; refresh your expired developer.apple.com login cookie at that site directly and then try again. (If you're reading this and you work for Apple, it's been a problem for several years, and it'd be truly swell if it showed a login page instead of an error page.)