Using tokens as login

What techniques are there to provide logins for current holders of a specific token?

One could do something like the Catalyst registration, which if I understand that correctly registers the public key of a key pair in the metadata of the registration transaction, while the private key is displayed as a QR code to be scanned by the Catalyst app.

But could it be more light-weight? Without transactions? Just using the private key of the holding address?

How do the various projects that want to use their tokens as voting power for governance do it?