Anyway, the point is not even that Twitter needs to be able to identify its users. Twitter just needs to get rid of its bot problem. To solve that problem, they could simply charge their users $5 and promise to refund if after some vetting period (by their fraud detection and other users). The downside of this approach, of course, is that it would deter not just bots but also a large number of legitimate users who wouldn't be interested in paying to sign-up.