chan_sip: Support auth username for callbackextension feature

ASTERISK-20527 #close

Change-Id: I659cf7f00836a09d09d146ad226a40477d731239

channels/chan_sip.c

@@ -31811,7 +31811,7 @@ static struct sip_peer *build_peer(const char *name, struct ast_variable *v, str
 	olddirectmediaacl = ast_free_acl_list(olddirectmediaacl);
 	if (!ast_strlen_zero(peer->callback)) { /* build string from peer info */
 		char *reg_string;
-		if (ast_asprintf(&reg_string, "%s?%s:%s@%s/%s", peer->name, peer->username, !ast_strlen_zero(peer->remotesecret) ? peer->remotesecret : peer->secret, peer->tohost, peer->callback) >= 0) {
+		if (ast_asprintf(&reg_string, "%s?%s:%s:%s@%s/%s", peer->name, S_OR(peer->fromuser, peer->username), S_OR(peer->remotesecret, peer->secret), peer->username, peer->tohost, peer->callback) >= 0) {
 			sip_register(reg_string, 0); /* XXX TODO: count in registry_count */
 			ast_free(reg_string);
 		}

configs/samples/sip.conf.sample

@@ -786,7 +786,7 @@ srvlookup=yes                   ; Enable DNS SRV lookups on outbound calls
 ; A similar effect can be achieved by adding a "callbackextension" option in a peer section.
 ; this is equivalent to having the following line in the general section:
 ;
-;        register => username:secret@host/callbackextension
+;        register => fromuser:secret:username@host/callbackextension
 ;
 ; and more readable because you don't have to write the parameters in two places
 ; (note that the "port" is ignored - this is a bug that should be fixed).