[Taek]

We're closer than I think you give us credit. The only major component we're missing is that normal browsers don't have the ability to verify that the portal is serving you the right code - which is of course super important.

Once you have that though, the rest can be done within the webapp itself. Credentials are managed by a separate webapp like https://sky-id.hns.siasky.net/, and some apps already have built in failover to try other portals if one is not responding.

With the advent of utreexo, it's even possible to run full blockchain nodes inside of a webapp. Again you need an integrity check on the code served by the portal, but if you have that you can independently do everything else.