[feat] use device keys for server login

apps/desktop/src/gui/runtime/device_login.h

@@ -0,0 +1,35 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2026-11-02
+ * Copyright (c) 2026 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _DEVICE_LOGIN_H_
+#define _DEVICE_LOGIN_H_
+
+#include <nlohmann/json.hpp>
+#include <string>
+
+#include "minirtc.h"
+
+namespace crossdesk {
+class TrustedDevices;
+
+// One signaling connection's application authentication, owned by its callbacks.
+class DeviceLogin {
+ public:
+  int Exchange(SignalExchangeStage stage, const nlohmann::json& message,
+               const TrustedDevices* identity, char* response, size_t capacity);
+  bool Pending() const { return phase_ != Phase::Idle; }
+  bool UsedPassword() const { return used_password_; }
+
+ private:
+  enum class Phase { Idle, AwaitingChallenge, AwaitingResult };
+  nlohmann::json request_;
+  std::string password_;
+  Phase phase_ = Phase::Idle;
+  bool used_password_ = false;
+};
+}  // namespace crossdesk
+
+#endif