he <b>pkey</b> argument must be the private key of the X.509 certificate <b>x</b>. If the <b>override</b> argument is 0, then <b>x</b>, <b>pkey</b> and <b>chain</b> are set only if all were not previously set. If <b>override</b> is non-0, then the certificate, private key and chain certs are always set. If <b>pkey</b> is NULL, then the public key of <b>x</b> is used as the private key. This is intended to be used with hardware (via the ENGINE interface) that stores the private key securely, such that it can