implement authentication via K_AUTH

[omar-polo]

This is the continuation of OpenSMTPD/OpenSMTPD-extras#64.

Since proc tables can know do the authentication themselves, it should be possible to handle K_AUTH, receive the plaintext password from smtpd and let the LDAP server do the authentication, instead of the current way of requiring the LDAP server to send us the hashed password.

[likle]

Hey @omar-polo, are you already working on this, or would you like some help with it? I currently see two small challenges in implementing this. First, I believe K_AUTH might not be usable yet, if that gets confirmed. Second, binding the user to verify the password could be problematic due to the single connection and asynchronous nature of table-ldap. One possible solution might be to open a new connection for each request?

[omar-polo]

Hello, sorry about the delay. I'm not actively working on ldap as I'm not really using it, I merely ported the existing code to the new way filters work by changing the API of the transport protocol. There is one user, that doesn't have a github account, but is active on both irc and the mailing list that is working quite a lot, which goes by the nickname "satanist".

I'd like to get the K_AUTH issue fixed as soon as possible, but for the other issue I can't really comment at the moment, I'm afraid.