Fix `use_identity_as_username true` not working.

Closes #833.

Thanks to David Crook and Brice Waegeneire.

Bug: https://github.com/eclipse/mosquitto/issues/833

Signed-off-by: Roger A. Light <roger@atchoo.org>

ChangeLog.txt

@@ -20,6 +20,7 @@ Broker:
   #209.
 - Fix bridge publishing failing when per_listener_settings was true. Closes
   #860.
+- Fix `use_identity_as_username true` not working. Closes #833.
 
 Library:
 - Fix some places where return codes were incorrect, including to the

src/handle_connect.c

@@ -455,6 +455,11 @@ int handle__connect(struct mosquitto_db *db, struct mosquitto *context)
 						goto handle_connect_error;
 					}
 					context->username = mosquitto__strdup((char *) ASN1_STRING_data(name_asn1));
+					if(!context->username){
+						send__connack(context, 0, CONNACK_REFUSED_SERVER_UNAVAILABLE);
+						rc = MOSQ_ERR_NOMEM;
+						goto handle_connect_error;
+					}
 					/* Make sure there isn't an embedded NUL character in the CN */
 					if ((size_t)ASN1_STRING_length(name_asn1) != strlen(context->username)) {
 						send__connack(context, 0, CONNACK_REFUSED_BAD_USERNAME_PASSWORD);