Architecture

[WhiteTomX]

We need to define the architecture:

• language
• framework
• architecture of the application
• hosting

[WhiteTomX]

There is the Microsoft Bot Framework for easy interacting with Teams. The Event notification can be done via Graph API and subscriptions.
I would like to have a application that can run Serverless on azure function to reduce costs. I expect that the webservices not realy need to run, but only react to income requests (Event Changes or User actions).
This introduces the problem of state, so how do we handle if we do changes and loosing some subscription.

[WhiteTomX]

Maybe an idea to get started: https://docs.microsoft.com/en-us/graph/tutorials/bot-framework?tutorial-step=5

Unfortunately with App Service and not Azure Functions, but maybe we can adopt this.
https://docs.microsoft.com/en-us/graph/webhooks

[WhiteTomX]

I created a overall picture how it could work in the first version (see 65f3668)
I propose two rather simple function. We will avoid delegated permissions in the beginning, as i suppose this is way harder than just using application permissions.

We don't need any conversation from Teams so this is a notificationBot only.

Management Function

This is a time triggered function. It will first check Table storage for the number of Eventsubscription we should have running. This number is compared to the actual subscriptions. If there is a missmatch, we delete the deltaLink from TableStorage

Next we will get the deltaLink from Table storage. If there is no delta Link we need to process all users instead. For each user we check if there is an valid subscription (correct Url). If not we create the subscription.

/Event Function

This is the HTTPS Endpoint to which the Graph API will send change Notification about events. We just relay the information to the user here.

Future changes

We could further improves this by also subscribing to User changes to subscripte to the users Events earlier. Furthermore we could change to delegated permissions, so only users that really want this functionality are included.