Function auth_usercheck 

pub unsafe extern "C" fn auth_usercheck(
    _name: *mut c_char,
    _style: *mut c_char,
    _type: *mut c_char,
    _password: *mut c_char,
) -> *mut auth_session_t

A single function interface to auth_userokay, but returns the opened BSD Authentication session

From authenticate(3):

The `auth_usercheck()` function operates the same as the `auth_userokay()` function except
that it does not close the BSD Authentication session created. Rather than returning the
status of the session, it returns a pointer to the newly created BSD Authentication
session.