Your Calendar Provider
Power Tags works by integrating with Microsoft or Google calendar API via a secure OAuth2 flow to detect tagged events. That's why users are asked to authenticate at Microsoft or Google.
Power Tags will request the following permissions from your provider:
Basic openid scopes (basic profile/email): This is the minimal set of standard permissions needed to authenticate a user.
Calendar read scopes: Power Tags uses these permissions to detect tagged events in your calendars. All other events are ignored.
(Microsoft only) MailboxSettings (timezone): Permission to obtain the time zone on Microsoft accounts.
Later on, if you decide to use certain tags such as email and teams tags to send emails and Teams messages from your calendar, you can grant additional consents to perform those actions.