[Dovecot] SSL Client Certificate Support

[Bert Koelewijn]

Dear Timo,

most modern enterprises make use of a Public Key Infrastructure. It 
would be nice to have dovecot check a client certificate instead of a 
password. This makes life much easier and more secure.
Mail clients like Mozilla and MS Outlook do support this. What do you 
think of the following feature request:

- Client authenticates with a certificate via SSL. (Like stunnel can)
- Dovecot looks the username up in a table with (public key, username)
- The mailclient gives a name and password, but dovecot ignores them
- Dovecot gives the client access by the username found in the table

This way existing mail clients can use this system and you can save your 
username with an empty password.

Best Regards,

Bert Koelewijn