MS Teams - Sending Messages to Users from External App

Question

The organization that I work for previously used Slack as our collaboration tool. With Slack, I was able to register an app in the workspace and use the provided access tokens to invoke the API to send a message to a user from our external web application. It was very straightforward. There was no intermediate app that needed to be coded to enable this messaging.

Recently, we've transitioned from Slack to MS Teams, and in looking over the Graph API documentation, there does not currently appear to be a way to proactively send a message from an external application to a user. The available permissions for the chatMessage endpoint indicate the availability of only a delegated permission to send a message on behalf of a specific user; no permission exists to send a message on behalf of an external application.

Is it possible to use the Graph API to directly send a message from an external application to a user? Or must a bot application be created in order to achieve this?

Answer 1

It must be a bot application to achieve above mentioned requirement. ChatMessage endpoint works to send a message on behalf of user only.