Vlad
Not working for me:
Tried it twice. Got the error each time:
If I edit the URL in the error page to remove the 'auth-ext', the page loads and I am logged in. I just downloaded/installed/updated the RC version, and had not logged into the proton.me account except via the ProtonPass extension, so it appears as if the extension is able to correctly authenticate me with proton, but fails somehow after that.