OpenSSH 5.4 added a new method for certificate authentication (changes).
* Add support for certificate authentication of users and hosts using a new, minimal OpenSSH certificate format (not X.509). Certificates contain a public key, identity information and some validity constraints and are signed with a standard SSH public key using ssh-keygen(1). CA keys may be marked as trusted in authorized_keys or via a TrustedUserCAKeys option in sshd_config(5) (for user authentication), or in known_hosts (for host authentication). Documentation for certificate support may be found in ssh-keygen(1), sshd(8) and ssh(1) and a description of the protocol extensions in PROTOCOL.certkeys.
Is there any guides or documentation beyond what is mentioned in the ssh-keygen man-page? The man page covers how to generate certificate and use them, but it doesn't really seem to provide much information about the certificate authority setup. For example, can I sign the keys with an intermediate CA, and have the server trust the parent CA?
This comment about the new feature seems to mean that I could setup my servers to trust the CA, then setup a method to sign keys, and then users would not have to publish their individual keys on the server. This also seems to support key expiration, which is great since getting rid of old/invalid keys is more difficult then it should be. But I am hoping to find some more documentation about describe the total configuration CA, SSH server, and SSH client settings needed to make this work.