OSSL_CRMF_CERTTEMPLATE_fill() sets those fields of the certTemplate I<tmpl>
for which non-NULL values are provided: I<pubkey>, I<subject>, I<issuer>,
and/or I<serial>.
+X.509 extensions may be set using OSSL_CRMF_MSG_set0_extensions().
On success the reference counter of the I<pubkey> (if given) is incremented,
while the I<subject>, I<issuer>, and I<serial> structures (if given) are copied.