Yesterday I was working on my APEX application running on Oracle Cloud, and I created also some additional users (for OCI and APEX). Then I tried to log in as those users and switched between them, but suddenly I couldn’t log in any more into my Cloud account.
The error message I got, was:
Bad Message 431
reason: Request Header Fields Too Large
The quick search via Google pointed out, the problem could be too much cookies (or too long cookie) for that site.
After I deleted the cookie for Oracle Cloud, then Sign In worked again.
Hope it will helps someone.