[asterisk-users] PJSIP not performing outbound authentication

[TTT]

I am using Asterisk 20.3.0 with PJSIP.  I have setup a trunk to my ISP
(Twilio) who requires outbound authentication.  My pjsip.auth.conf contains:

[Twilio]
type=auth
auth_type=userpass
password=mysecret
username=myun

However, my calls using the trunk are rejected with a 403. Using pjsip
logging I notice that the outgoing invite does not have an authentication
line. Why is Asterisk not sending credentials to the ISP? SIP transactions
are:
 > INVITE
 < 100 TRYING
 < 403 FORBIDDEN

Or is this normal?  Must Twilio respond with a 407 which will cause Asterisk
to authenticate?