Use start_realm cc config in export cred

lib/gssapi/krb5/creds.c

@@ -62,16 +62,35 @@ _gsskrb5_export_cred(OM_uint32 *minor_status,
     type = krb5_cc_get_type(context, handle->ccache);
     if (strcmp(type, "MEMORY") == 0) {
 	krb5_creds *creds;
+	krb5_data config_start_realm;
+	char *start_realm;
+
 	ret = krb5_store_uint32(sp, 0);
 	if (ret) {
 	    krb5_storage_free(sp);
 	    *minor_status = ret;
 	    return GSS_S_FAILURE;
 	}
 
-	ret = _krb5_get_krbtgt(context, handle->ccache,
-			       handle->principal->realm,
-			       &creds);
+	ret = krb5_cc_get_config(context, handle->ccache, NULL, "start_realm",
+				 &config_start_realm);
+	if (ret == 0) {
+	    start_realm = strndup(config_start_realm.data,
+				  config_start_realm.length);
+	    krb5_data_free(&config_start_realm);
+	} else {
+	    start_realm = strdup(krb5_principal_get_realm(context,
+							  handle->principal));
+	}
+	if (start_realm == NULL) {
+	    *minor_status = krb5_enomem(context);
+	    krb5_storage_free(sp);
+	    return GSS_S_FAILURE;
+	}
+
+	ret = _krb5_get_krbtgt(context, handle->ccache, start_realm, &creds);
+	free(start_realm);
+	start_realm = NULL;
 	if (ret) {
 	    krb5_storage_free(sp);
 	    *minor_status = ret;