Why is Mac OS asking me to permit it total control over my Gmail?

I just updated to Mojave and a pop-up said I need to enter my password for my Gmail account. But when I clicked on the window, it said I had to do it in Safari (huh, ***?), so I opened Safari, and not only does it want me to enter my password, but wants permission to compose, send, delete emails, read all of them, etc, etc,! This is not cool, and especially when it offers zero explanation as to why this outrageous request is made, as I've never, ever done that before. Anyone know why this has occurred?

Here's what it wants:

Sign in with Google

macOS wants to access your Google Account

This will allow macOS to:

Read, compose, send, and permanently delete all your email from Gmail

See, edit, download, and permanently delete your contacts

See, edit, share, and permanently delete all the calendars you can access using Google Calendar

View and send chat messages

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[Email Edited by Moderator]