openssh

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/

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