THIS CONFIG WORKS!
Mine IS authenticating (much like an IP auth but with a dynamic hostname). Mine actually is configured on Elastix , and Here is what I have in the trunk
name trunkName
details:
host=my.ddns.com
port=5092
type=peer
insecure=port,invite
canreinvite=no
directmedia=no
disallow=all
allow=ulaw&ilbc
context=from-pstn
trustrpid=yes
qualify=yes
user settings TrunkName-in
insecure=port,invite
disallow=all
allow=ulaw&ilbc
canreinvite=no
directmedia=no
context=from-pstn
trustrpid=yes
port=5092
Other settings that may have an impact:
if using a dynamic hostname , edit /etc/asterisk dnsmanager.conf and avtivate it by commenting out lines and changing updates to 60. This ensures that ddns hostname is not stale
Asterisk SIP settngs at bottom of page in the blank fields add:
match_auth_username = yes
As I can not get to the grandstream at the moment I can not post the HT503 config here now but maybe later. If you do not authenticate you need to enable anonymous SIP inbounds which I only recommend to my worst enemies.
I can say that the grandstream shares the username and password that is used in asterisk and points to the asterisk IP with the call forward settings configured to destination@asteriskIP.
Mark