Help with CA Certificates for user authentication?

[Ángel González]

Iain Morgan wrote:
> Using certificates does not bypass the need for a passphrase. For both
> certificate and public-key authentication, the candidate key or
> certificate is first presented to the server to see if it will be
> accepted. If the server is willing to accept the key or cert, you then
> move on to the stage where an actual signature is required.
>
> Note that just as with conventional public-key authentication, you can
> use ssh-agent to avoid having to enter the passphrase every time.

I guess it should be equally possible to use a passwordless file...