On Fri, 22 Mar 2013 OpenSSH 6.2 was released and like always, bring more improvements including support for multiple required authentication in SSH
protocol 2 via an AuthenticationMethods option:
sshd(8): Added support for multiple required authentication in SSH protocol 2 via an AuthenticationMethods option. This option lists one or more comma-separated lists of authentication method names. Successful completion of all the methods in any list is required for authentication to complete. This allows, for example, requiring a user having to authenticate via public key or GSSAPI before they are offered password authentication.
You can read more about this release here: https://lwn.net/Articles/543961/