Fix KDC client referrals

Although our built-in KDB modules do not support client referrals for
AS requests, the KDC is supposed to return one if a third-party module
returns a DB entry containing a principal in a foreign realm.
Unfortunately, this code has never worked; in prepare_error_as(), we
erroneously compare the protocol code errcode against the com_err code
KRB5KDC_ERR_WRONG_REALM; as a result, we never supply the canonical
client principal.  Fix this by comparing errcode against the protocol
code KDC_ERR_WRONG_REALM instead.

Discovered by Alexander Bokovoy and Simo Sorce.

(cherry picked from commit 4e036ef)

ticket: 8312 (new)
version_fixed: 1.12.5
status: resolved

src/kdc/do_as_req.c

@@ -805,7 +805,7 @@ prepare_error_as (struct kdc_request_state *rstate, krb5_kdc_req *request,
         return retval;
     errpkt.error = error;
     errpkt.server = request->server;
-    errpkt.client = (error == KRB5KDC_ERR_WRONG_REALM) ? canon_client :
+    errpkt.client = (error == KDC_ERR_WRONG_REALM) ? canon_client :
         request->client;
     errpkt.text = string2data((char *)status);