I would look at implementing this using some sort of SSO (single sign-on) scheme. That gets around the problem of having to install new client software.
One obvious problem with all such schemes is how to prevent actors from gaming the system, e.g., to get free logins for self + a bunch of friends. I
The downside is the high entry bar of installing a new browser and setting up a cryptocurrency wallet (payments are made with Basic Attention Tokens).