An idea for publishing presence data from Teams to various subscribers. This way a single polling mechanism can send to n clients with a single poller. Eventually presence will get push/change notification support in graph.
You'll need the Presence.Read permission, which requires admin consent - something that may be difficult to come by.
This example is slightly different in that the function itself is handling the interactivity & token acquisition, caching tokens in MSAL in Table storage. The authorization URL is generated, including offline_access to get a refresh token, the user is redirected, then we consume the authorization_code via msal on the return trip. No implicit! This is all form_post.
Once the tokens are acquired, it starts polling every 30 seconds for new changes to presence. There's a balance here - 30 seconds is sorta slow but running a timer function every second might be more than you're willing to spend ($0.40 at last check, for ~2.6m executions). Cost consideration is probably more important around storage txns rather than function execution, since msal's token cache accessors access more than once on a single retrieval - so each run is ~3-4 storage txns.
More on the token cache - the token cache should be per user in msal, but we lack an effective way to know the user without a hydrated Account - it's sort of chicken and egg, although not really - things like login_hint could be used, since this is background work that doesn't have a user issuing actual requests to it - but more on that later.
This is sort of a mess - since there is no way I can see to use a cache lookup key per request, instead I've gone with the nuclear option of transient CCAs for each user, with a wrapper around the BeforeAccess and AfterAccess setters to configure them to a specific key. It's messy and I really don't like constantly creating and trashing those CCAs, but it's 2020 and memory is cheap, i guess :/