Last tested: Oct 2, 2020
When trying to access pages on your Looker instance, you may get a mostly blank page with a 403 and the error message
You are not authorized to view this page:
This most likely means you started an embed user session in this browser window. Looker can't maintain multiple user sessions in the same window, so starting the embed user session ended your regular user session. Since embed users cannot view non-embed pages in the UI, you will see a 403 error if you attempt to navigate to those pages. You can log in as your regular user again by entering [base_url]/login into the browser bar, which will take you directly to the login page.
This is a common situation for users who are trying out SSO embed for the first time, especially when testing using the Preview in Fabio's tool. It is recommended to do your SSO embed testing in a different browser or incognito window to avoid interrupting your regular Looker user session.