Man pages matching name mongoc_uri_get_auth_source in section 3:

mongoc_uri_get_auth_source.3.en	debian 10 / libmongoc-doc
mongoc_uri_get_auth_source.3.en	debian 11 / libmongoc-doc
mongoc_uri_get_auth_source.3.en	debian 12 / libmongoc-doc