It would be really helpful to have passport intrgrated as internal authentication middleware.
It allows us:
1) to keep current behaviour by passport.authenticate('local') strategy.
2) to have a lot of authentication mechanisms (over 300) https://github.com/jaredhanson/passport#strategies-1
For example:
var OpenIDStrategy = require('passport-openid').Strategy;
keystone.passport.use(new OpenIDStrategy({ ... }));