I vote by mail in CA permanently, so there is no ID required at time of voting. Registration requires CA Lic# and last four digits of Soc. Sec along with the other stuff. They use the CA. License for a signature on file. When the ballot is received that is compared with my signature on the ballot envelope.
However, my registration can be contested if the registrar wishes proof of ID. The electoral rolls indicate I do a mail in ballot, so I cannot vote at the polling place except by a provisional ballot. They use a special envelope for those. For instance I think it was mailed too late. lost the mail in ballot, or I moved. They will cancel the mail in ballot.
To add fuel to the debate consider "Gov. Jerry Brown signed legislation Thursday allowing Sacramento and 13 other counties to eliminate most neighborhood polling places and send ballots to all voters starting in 2018. Sacramento County Registrar of Voters Jill LaVine said this week that she hopes to shift voters toward a mail ballot system in two years."