sconn, chans, reqs, err := ssh.NewServerConn(conn, cfg)
if err != nil {
    return
}

// Handle [email protected] and [email protected]
reqs, err = sshext.UpdateHostKeys(sconn, reqs, signers)
// Handle [email protected]
reqs, noMore, err = sshext.NoMoreSessions(reqs)

go ssh.DiscardRequests(reqs)

for c := range chans {
    if c.ChannelType() == "session" {
        select {
        case <-noMore:
            sconn.Close()
        default:
            // handle session channel
        }
    }
}