[out-of-ideas]

the same thing hacker news uses; a user name and a password.

if we want proof that each account correlates to exactly one person, well i think that should 100% not be a phone number and is an entierly bigger+different problem

[lxgr]

I fully agree, but practically, this is what many companies are doing right now.

[out-of-ideas]

lol after what we've just seen, when one company jumps off a bridge and lays off a ton of folks, other companies copy that same move...