feat: install code of 3 to 24 letters and digits with a button to make a new one; guesses are limited per address

internal/server/handlers_panel.go

@@ -410,6 +410,7 @@ func (s *Server) handleSettings(w http.ResponseWriter, r *http.Request) {
 		"Admin":         s.currentAdmin(r),
 		"Host":          host,
 		"Secret":        secret,
+		"CodeLen":       s.db.InstallCodeLen(),
 		"Admins":        admins,
 		"KeyCounts":     keyCounts,
 		"PassOff":       passOff,
@@ -516,7 +517,22 @@ func (s *Server) handleRotateSecret(w http.ResponseWriter, r *http.Request) {
 	}
 	_ = s.db.SetConfig(cfgEnrollSecret, randToken())
 	// Rotate the short install code too so old /i/<code> links stop working.
-	_ = s.db.SetConfig(cfgInstallCode, shortCode())
+	_ = s.db.SetConfig(cfgInstallCode, shortCode(s.db.InstallCodeLen()))
+	http.Redirect(w, r, "/settings", http.StatusSeeOther)
+}
+
+// POST /settings/install/code - a new install code, of the length given:
+// the old /i/<code> link stops working.
+func (s *Server) handleInstallCode(w http.ResponseWriter, r *http.Request) {
+	if !checkCSRF(r) {
+		http.Error(w, "bad csrf", http.StatusForbidden)
+		return
+	}
+	if n, err := strconv.Atoi(r.FormValue("len")); err == nil {
+		n = min(installCodeMax, max(installCodeMin, n))
+		_ = s.db.SetConfig(cfgInstallLen, strconv.Itoa(n))
+	}
+	_ = s.db.SetConfig(cfgInstallCode, shortCode(s.db.InstallCodeLen()))
 	http.Redirect(w, r, "/settings", http.StatusSeeOther)
 }
 
@@ -603,9 +619,17 @@ func (s *Server) handleInstallScript(w http.ResponseWriter, r *http.Request) {
 //
 //	wget -qO- https://host/i/<code> | sudo sh
 func (s *Server) handleShortInstall(w http.ResponseWriter, r *http.Request) {
+	// A short code can be guessed: wrong ones count against the address
+	// like wrong passwords do.
+	ip := clientIP(r)
+	if s.limiter.blocked(ip) {
+		http.Error(w, "too many attempts", http.StatusTooManyRequests)
+		return
+	}
 	code := r.PathValue("code")
 	want := s.db.InstallCode()
 	if want == "" || !constantTimeEqual(code, want) {
+		s.limiter.fin(ip, false)
 		http.NotFound(w, r)
 		return
 	}