Direct Line API is part of Microsoft's Bot Framework and is one of the available messaging channels there, along with Facebook, Skype etc. It enables access to the bot created using that framework from any custom app or webpage.
The Bot Framework REST APIs enable you to build bots that exchange messages with channels configured in the Bot Framework Portal, store and retrieve state data, and connect your own client applications to your bots. All Bot Framework services use industry-standard REST and JSON over HTTPS.
You can enable your own client application to communicate with your bot by using the Direct Line API. The Direct Line API implements an authentication mechanism that uses standard secret/token patterns and provides a stable schema, even if your bot changes its protocol version.
