Added logging about authentication errors.

server/modules/protocol/mysql_common.c

@@ -1537,6 +1537,12 @@ int gw_find_mysql_user_password_sha1(char *username, uint8_t *gateway_password,
 					      pthread_self(),
 					      key.user,
 					      dcb->remote)));
+
+			    skygw_log_write_flush(
+				    LOGFILE_ERROR,
+					     "Authentication Failed: user [%s@%s] not found.",
+					     key.user,
+					     dcb->remote);
 			    break;
 			}