Asterisk PJSIP endpoint identification by To number

Recently got an interesting task.

For calls, that are made to a specific number, apply DTMF transcoding towards caller side. Means when someone (an automated system, actually) answers on this specific number, it starts send DTMF codes towards caller. But the main issue as, that callers, that are calling to this number accept DTMF only in inband mode, despite that looking on SIP traces they should accept usual RFC4733.

DTMF transcoding (in PJSIP) is handled by Asterisk via endpoint parameters. So, all calls ONLY to this number need to be put into a specific endpoint. Gladly, it's not so hard to achieve, but the documentation is lacking examples. So, here is the one:

pjsip.conf

[global]
...
# Depending on your configuration you might need to adjust the order
endpoint_identifier_order=ip,username,header,anonymous

# Actual endpoint we need call to be placed FROM
[test_endpoint]
type=endpoint
...
dtmf_mode=inband
identify_by=header

[test_endpoint]
type=identify
endpoint=test_endpoint
match_header=To:/123456789/

Now all calls made to a number, that consists sequence 123456789 will be made from test_endpoint and all DTMF towards this endpoint will be transcoded to inband.