Function login_cap_sys::login_getstyle

pub unsafe extern "C" fn login_getstyle(
    _lc: *mut login_cap_t, 
    _style: *mut c_char, 
    _type: *mut c_char
) -> *mut c_char

From login_getclass(3):

The login_getstyle() function is used to obtain
the style of authentication that should be used for this user class.  The
style argument may either be NULL or the desired style of authentication.
If NULL, the first available authentication style will be used.  The type
argument refers to the type of authentication being performed.  This is
used to override the standard auth entry in the database.  By convention
this should be of the form "auth-type".  Future releases may remove the
requirement for the "auth-" prefix and add it if it is missing.  If type
is NULL then only "auth" will be looked at (see login.conf(5)).  The
login_getstyle() function will return NULL if the desired style of
authentication is not available, or if no style is available.