KEYS: Allow authentication data to be stored in an asymmetric key

Allow authentication data to be stored in an asymmetric key in the 4th
element of the key payload and provide a way for it to be destroyed.

For the public key subtype, this will be a public_key_signature struct.

Signed-off-by: David Howells <dhowells@redhat.com>

crypto/asymmetric_keys/x509_cert_parser.c

@@ -47,7 +47,7 @@ struct x509_parse_context {
 void x509_free_certificate(struct x509_certificate *cert)
 {
 	if (cert) {
-		public_key_destroy(cert->pub);
+		public_key_free(cert->pub);
 		kfree(cert->issuer);
 		kfree(cert->subject);
 		kfree(cert->id);