I have reproduced with multiple browsers (Edge, IE, Chrome) using multiple tenants with multiple accounts (Global Admins, Service Admins, PowerApps user).
Steps to reproduce:
(let's pretend we have two tenants named ContosoA & ContosoB)
- Go to https://web.powerapps.com
- Log in with credentials for ContosoA
- Go to upper-right user icon and click to open the drop down
- Click on "Sign Out"
- Wait for the sign out process to complete
- Close all browser windows (including those not being used for PowerApps)
- Open browser again and go to https://web.powerapps.com
After Step #7 there is no prompt to login. I am taken directly to my PowerApps workspace and allowed all the same access even though I formally signed-out and closed all browsers. There is no prompt to reauthenticate.
To continue, I found this works in both directions (which is the really scary part for developers)
- Repeat steps 3-6
- Open browser and go to https://ContosoB.sharepoint.com
- Verify you are logged in with correct accout for ContosoB as expected (so far, so good)
- Click the waffle in the upper-left corner and selec the app PowerApps
- Wait the new tab containing the PowerApps workspace to load
- Look at the upper-right corner and see the account currently logged in for PowerApps
- Is it for ContosoB (as it should be) or is it for ContosoA?
For me, it's the latter. This doesn't happen using InPrivate browsing, so that's at least something. The bigger issue is, since I manually signed-out, it should at least be prompting me to sign in again. But that is not happening.