The random order in which cert_parse_pre's switch handles extensions
has confused me too many times. I'd like this to match the order in
RFC 6487, section 4.8. This isn't perfect either - ski comes before aki
and aia comes before sia. Still, it's better.

To make this easy to review, I'll do it in a couple of steps. Here's
the first one, covering sections 4.8.1-4.8.7.

       4.8.1.  Basic Constraints  . . . . . . . . . . . . . . . . . .  8
       4.8.2.  Subject Key Identifier . . . . . . . . . . . . . . . .  9
       4.8.3.  Authority Key Identifier . . . . . . . . . . . . . . .  9
       4.8.4.  Key Usage  . . . . . . . . . . . . . . . . . . . . . .  9
       4.8.5.  Extended Key Usage . . . . . . . . . . . . . . . . . .  9
       4.8.6.  CRL Distribution Points  . . . . . . . . . . . . . . . 10
       4.8.7.  Authority Information Access . . . . . . . . . . . . . 10

Index: cert.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/cert.c,v
diff -u -p -r1.159 cert.c
--- cert.c	4 Jun 2025 09:18:28 -0000	1.159
+++ cert.c	18 Jun 2025 22:49:14 -0000
@@ -881,6 +881,34 @@ cert_parse_pre(const char *fn, const uns
 		assert(obj != NULL);
 
 		switch (nid = OBJ_obj2nid(obj)) {
+		case NID_basic_constraints:
+			if (bc++ > 0)
+				goto dup;
+			break;
+		case NID_subject_key_identifier:
+			if (ski++ > 0)
+				goto dup;
+			break;
+		case NID_authority_key_identifier:
+			if (aki++ > 0)
+				goto dup;
+			break;
+		case NID_key_usage:
+			if (ku++ > 0)
+				goto dup;
+			break;
+		case NID_ext_key_usage:
+			if (eku++ > 0)
+				goto dup;
+			break;
+		case NID_crl_distribution_points:
+			if (crldp++ > 0)
+				goto dup;
+			break;
+		case NID_info_access:
+			if (aia++ > 0)
+				goto dup;
+			break;
 		case NID_sbgp_ipAddrBlock:
 			if (ip++ > 0)
 				goto dup;
@@ -908,34 +936,6 @@ cert_parse_pre(const char *fn, const uns
 				goto dup;
 			if (!certificate_policies(fn, cert, ext))
 				goto out;
-			break;
-		case NID_crl_distribution_points:
-			if (crldp++ > 0)
-				goto dup;
-			break;
-		case NID_info_access:
-			if (aia++ > 0)
-				goto dup;
-			break;
-		case NID_authority_key_identifier:
-			if (aki++ > 0)
-				goto dup;
-			break;
-		case NID_subject_key_identifier:
-			if (ski++ > 0)
-				goto dup;
-			break;
-		case NID_ext_key_usage:
-			if (eku++ > 0)
-				goto dup;
-			break;
-		case NID_basic_constraints:
-			if (bc++ > 0)
-				goto dup;
-			break;
-		case NID_key_usage:
-			if (ku++ > 0)
-				goto dup;
 			break;
 		default:
 			/* unexpected extensions warrant investigation */