Man pages matching name curlopt_xoauth2_bearer in section 3:

CURLOPT_XOAUTH2_BEARER.3.en	debian 10 / libcurl4-doc
CURLOPT_XOAUTH2_BEARER.3.en	debian 11 / libcurl4-doc
CURLOPT_XOAUTH2_BEARER.3.en	debian 12 / libcurl4-doc