How to implement PPP interface on ESP32 with SIM800L modem?

I have a project on an ESP32 that runs on wi-fi, I need to add a modem e.g. SIM800L.
I have searched the internets and can't find a library/tutorial anywhere on the subject of implementing the ppp interface.

I can't use the built-in mechanism based on AT commands because my communication protocol is quite customised
and not based on http/https.

Hence the question: has anyone managed to do this, or seen a similar solution somewhere on the internet.

It looks like the modem supports such a communication mode, as it works for example on Raspberry Pi and other Linuxes.

Greetings

coyot wrote:

I have searched the internets and nowhere can I find a library/tutorial on the subject of ppp interface implementation.

.
It's in the examples, in the ESP-IDF sources:
https://github.com/espressif/esp-idf/tree/master/examples/protocols/pppos_client

This appears to be just what I needed.
I need some advice on how to painlessly "implant" this into a project on an Arduino.