I'm sorry, but I have no experience in the field. My idea is device with any ARM (maybe STM32F107) connected to the Internet and communicating with Telegram messaging client over HTTPS interface as Boot (over Bot API)
This is relatively simple Telegram implement GET and POST any as api.telegram.org/.../METHOD_NAME more more information core.telegram.org/.../api
I look on MDK-Professional Middleware for IPv4 and IPv6 Networking http://www.keil.com/pack/doc/mw/Network/html/index.html and mbed TLS software component for TLS Layer www.keil.com/.../secure_communication.html
Unfortunately, I do not know how to grasp it all. Best would be to find an example of communicating with https