refactor: simplify the code

GPClient/standardloginwindow.h

@@ -0,0 +1,33 @@
+#ifndef STANDARDLOGINWINDOW_H
+#define STANDARDLOGINWINDOW_H
+
+#include <QtWidgets/QDialog>
+
+namespace Ui {
+    class StandardLoginWindow;
+}
+
+class StandardLoginWindow : public QDialog {
+Q_OBJECT
+
+public:
+    explicit StandardLoginWindow(const QString &portalAddress, const QString &labelUsername,
+                                 const QString &labelPassword, const QString &authMessage);
+
+    void setProcessing(bool isProcessing);
+
+private slots:
+
+    void on_loginButton_clicked();
+
+signals:
+
+    void performLogin(QString username, QString password);
+
+private:
+    Ui::StandardLoginWindow *ui;
+
+    void closeEvent(QCloseEvent *event);
+};
+
+#endif // STANDARDLOGINWINDOW_H