Man pages matching name curlopt_disallow_username_in_url in section 3:

CURLOPT_DISALLOW_USERNAME_IN_URL.3.en	debian 10 / libcurl4-doc
CURLOPT_DISALLOW_USERNAME_IN_URL.3.en	debian 11 / libcurl4-doc
CURLOPT_DISALLOW_USERNAME_IN_URL.3.en	debian 12 / libcurl4-doc