Add ConnectionFailedCallback to enable reporting of failed connection

server.go

@@ -48,6 +48,8 @@ type Server struct {
 	ServerConfigCallback          ServerConfigCallback          // callback for configuring detailed SSH options
 	SessionRequestCallback        SessionRequestCallback        // callback for allowing or denying SSH sessions
 
+	ConnectionFailedCallback ConnectionFailedCallback // callback to report connection failures
+
 	IdleTimeout time.Duration // connection timeout when no activity, none if empty
 	MaxTimeout  time.Duration // absolute connection timeout, none if empty
 
@@ -278,7 +280,9 @@ func (srv *Server) HandleConn(newConn net.Conn) {
 	defer conn.Close()
 	sshConn, chans, reqs, err := gossh.NewServerConn(conn, srv.config(ctx))
 	if err != nil {
-		// TODO: trigger event callback
+		if srv.ConnectionFailedCallback != nil {
+			srv.ConnectionFailedCallback(conn, err)
+		}
 		return
 	}
 

ssh.go

@@ -64,6 +64,10 @@ type ReversePortForwardingCallback func(ctx Context, bindHost string, bindPort u
 // ServerConfigCallback is a hook for creating custom default server configs
 type ServerConfigCallback func(ctx Context) *gossh.ServerConfig
 
+// ConnectionFailedCallback is a hook for reporting failed connections
+// Please note: the net.Conn is likely to be closed at this point
+type ConnectionFailedCallback func(conn net.Conn, err error)
+
 // Window represents the size of a PTY window.
 type Window struct {
 	Width  int