Is it possible to use the AUTH access token we got back from MSAL on a mobile app to open an office365 page in the browser, like mail or calendar, etc. without having to re-auth the user? I can send the token in the header, but can't find any requirements specs out there.
This is not possible today: the token you get from AAD is for your app - not for Office. In addition, users may be logged on the browser for example with a user that is different than the user signed-in to your application.