ssh/tailssh: add support for sending multiple banners

Signed-off-by: Maisem Ali <maisem@tailscale.com>

tempfork/gliderlabs/ssh/context.go

@@ -55,6 +55,8 @@ var (
 	// ContextKeyPublicKey is a context key for use with Contexts in this package.
 	// The associated value will be of type PublicKey.
 	ContextKeyPublicKey = &contextKey{"public-key"}
+
+	ContextKeySendAuthBanner = &contextKey{"send-auth-banner"}
 )
 
 // Context is a package specific context interface. It exposes connection
@@ -89,6 +91,8 @@ type Context interface {
 
 	// SetValue allows you to easily write new values into the underlying context.
 	SetValue(key, value interface{})
+
+	SendAuthBanner(banner string) error
 }
 
 type sshContext struct {
@@ -117,6 +121,7 @@ func applyConnMetadata(ctx Context, conn gossh.ConnMetadata) {
 	ctx.SetValue(ContextKeyUser, conn.User())
 	ctx.SetValue(ContextKeyLocalAddr, conn.LocalAddr())
 	ctx.SetValue(ContextKeyRemoteAddr, conn.RemoteAddr())
+	ctx.SetValue(ContextKeySendAuthBanner, conn.SendAuthBanner)
 }
 
 func (ctx *sshContext) SetValue(key, value interface{}) {
@@ -153,3 +158,7 @@ func (ctx *sshContext) LocalAddr() net.Addr {
 func (ctx *sshContext) Permissions() *Permissions {
 	return ctx.Value(ContextKeyPermissions).(*Permissions)
 }
+
+func (ctx *sshContext) SendAuthBanner(msg string) error {
+	return ctx.Value(ContextKeySendAuthBanner).(func(string) error)(msg)
+}

tempfork/gliderlabs/ssh/server.go

@@ -38,8 +38,7 @@ type Server struct {
 	HostSigners []Signer // private keys for the host key, must have at least one
 	Version     string   // server version to be sent before the initial handshake
 
-	KeyboardInteractiveHandler    KeyboardInteractiveHandler // keyboard-interactive authentication handler
-	BannerHandler                 BannerHandler
+	KeyboardInteractiveHandler    KeyboardInteractiveHandler    // keyboard-interactive authentication handler
 	PasswordHandler               PasswordHandler               // password authentication handler
 	PublicKeyHandler              PublicKeyHandler              // public key authentication handler
 	NoClientAuthHandler           NoClientAuthHandler           // no client authentication handler
@@ -171,12 +170,6 @@ func (srv *Server) config(ctx Context) *gossh.ServerConfig {
 			return ctx.Permissions().Permissions, nil
 		}
 	}
-	if srv.BannerHandler != nil {
-		config.BannerCallback = func(conn gossh.ConnMetadata) string {
-			applyConnMetadata(ctx, conn)
-			return srv.BannerHandler(ctx)
-		}
-	}
 	return config
 }