successful a pointer to the B<X509> structure is returned. If an error
occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
returned structure is written to B<*px>. If B<*px> is not B<NULL>
then it is assumed that B<*px> contains a valid B<X509>
structure and an attempt is made to reuse it. If the call is
successful a pointer to the B<X509> structure is returned. If an error
occurred then B<NULL> is returned. If B<px> is not B<NULL> then the
returned structure is written to B<*px>. If B<*px> is not B<NULL>
then it is assumed that B<*px> contains a valid B<X509>
structure and an attempt is made to reuse it. If the call is