Allocate an ASN.1 scan context with the given per-field scan callback.
Declared in <openssl/asn1.h>
<openssl/asn1.h>
ASN1_SCTX* ASN1_SCTX_new(int(* scan_cb)(ASN1_SCTX*));
New ASN1_SCTX, or NULL on allocation failure; free with ASN1_SCTX_free().