0365 APP KEY authorisation for shared channel set up

The ability to authorise shared O365 channels via an O365 app token instead of going through our current flow which uses delegated permissions via OAUTH.

From 0365:

1. Delegated Permissions. Enables your client app to perform operations on behalf of the signed-in user, such as reading email or modifying the user's profile.

2. Application Permissions. Permissions that enable the client app to authenticate as itself without user interaction or consent, such as an app used by background services or daemon apps.Source: O365