which browser security features do you find the hardest to use correctly?

very interested in "other" responses too, I could only include 4 options in the poll

CORS
51.6%
Cookie security settings (HttpOnly etc)
5.3%
Content-Security-Policy
41%
Other
2.2%
Poll ended at .
@b0rk Voted CORS because people forget that browser will perform the actual network request in non-preflight requests, the client just can't read the result (this often used to lead to CSRF before samesite cookies adoption).