Cloud-based messaging app Telegram provides free, open and secure communication across any platform with automatic chat synching across devices. Telegram also provides a dedicated Bot API for building custom bots that users can interact with via messages and commands to perform predefined tasks.
There are three standard ways to manage API authentication these days: API keys, OAuth tokens and JSON Web tokens (JWT). Adam Duvander over at the Zapier engineering blog explains how and when to use them. The humble API key is the common and earliest form of API authentication.