The stated (and valid) concern is that malicious actors would use fraudulent branding on those browser auth popups — let’s tell the user we are MSFT or AAPL and steal their password.
One solution is for the branding to consist entirely of NFT assets that can all be tracked to a definitive owner, and use some DNS-based glue (ala DKIM/SPIF for email) to link the NFT to the TLD.
Then your browser can refuse to show the MSFT logo (and show a big red fraud alert page) if the owner of the branding can’t be reliably traced back to Microsoft (owner of the site).