Always treat anonymous as preauth required

Always treat the WELLKNOWN/ANONYMOUS principal as requiring pre-authentication.  The anonymous draft depends on a pre-auth exchange to invoke pkinit.

ticket: 6623
target_version: 1.8
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23603 dc483132-0cff-0310-8789-dd5450dbe970

src/kdc/do_as_req.c

@@ -407,6 +407,7 @@ process_as_req(krb5_kdc_req *request, krb5_data *req_pkt,
             goto errout;
         }
         enc_tkt_reply.client = request->client;
+        setflag(client.attributes, KRB5_KDB_REQUIRES_PRE_AUTH);
     }
     /*
      * Check the preauthentication if it is there.