[wmf]

This already exists, but the UX is terrible and there's a chicken-and-egg problem in getting it fixed in every (deployed) browser.

http://www.gnegg.ch/2008/05/why-is-nobody-using-ssl-client-c...

[joeyespo]

Yeah, even using them over at GitHub (well, pushing with Git over SSH in general) has proven to be a rather steep learning curve for a lot of people. But hey, it's being widely adopted there, so that's a step in the right direction for this.