#1 - March 17, 2012, 2:25 a.m.
Blizzard Post
As of Beta Patch 15, Battle.net Authenticators have been enabled for the Diablo III beta test. If you have a Blizzard Authenticator attached to your Battle.net account, you will be prompted to enter an authentication code when logging into the beta client.

Please note that, after your first successful login with an Authenticator, you may not always receive an authenticator prompt when logging into the game. Not to worry! This is an intended convenience feature and doesn't represent a risk to your security. If you're logging in consistently from the same location, you may not be prompted for an authenticator code.