Allow exporting secret keys.

Requests the passphrase with a popup.

As from GPGME 1.15.0, the loopback pinentry is functional when exporting secret keys. It works fine when the exact passphrase is provided. If it's a wrong passphrase, GPGME does not generate an ::Error, but the app crashes with 'free(): double free detected in tcache 2'.

Hence, this patch cannot be committed to master.

Status : dangerous
Result : works and works not
Reason : a wrong passphrase means a crash

PopupExportSecretKey.cpp

@@ -0,0 +1,58 @@
+/* 
+ * File:   PopupExportSecretKey.cpp
+ * Author: SET - nmset@yandex.com
+ * License : GPL v2
+ * Copyright SET - © 2019
+ * 
+ * Created on November 19, 2020, 9:01 PM
+ */
+
+#include "PopupExportSecretKey.h"
+#include <Wt/WVBoxLayout.h>
+#include <Wt/WHBoxLayout.h>
+#include "global.h"
+
+PopupExportSecretKey::PopupExportSecretKey(WWidget * anchorWidget,
+                                           TransientMessageWidget * txtMessage,
+                                           const WLength& width)
+: WPopupWidget(cpp14::make_unique<WContainerWidget>())
+{
+    m_tmwMessage = txtMessage;
+    m_cwMain = NULL;
+    m_lblPassphrase = NULL;
+    m_lePassphrase = NULL;
+    m_btnPreApply = NULL;
+    m_btnApply = NULL;
+    
+    setTransient(true);
+    setAnchorWidget(anchorWidget);
+    setWidth(width);
+}
+
+PopupExportSecretKey::~PopupExportSecretKey()
+{
+}
+
+void PopupExportSecretKey::Create()
+{
+    m_cwMain = static_cast<WContainerWidget*> (implementation());
+    m_cwMain->setStyleClass("popup");
+
+    WVBoxLayout * vblMain = new WVBoxLayout();
+    m_cwMain->setLayout(unique_ptr<WVBoxLayout> (vblMain));
+    WHBoxLayout * hblPassphrase = new WHBoxLayout();
+    m_lblPassphrase = new WText(TR("Passphrase"));
+    hblPassphrase->addWidget(unique_ptr<WText> (m_lblPassphrase));
+    m_lePassphrase = new WLineEdit();
+    m_lePassphrase->setEchoMode(EchoMode::Password);
+    hblPassphrase->addWidget(unique_ptr<WLineEdit> (m_lePassphrase));
+    vblMain->addLayout(unique_ptr<WHBoxLayout> (hblPassphrase));
+    
+    m_btnPreApply = new WPushButton(TR("PreExportSecretKey"));
+    vblMain->addWidget(unique_ptr<WPushButton> (m_btnPreApply));
+    m_btnApply = new WPushButton(TR("ExportSecretKey"));
+    m_btnApply->setToolTip(TR("TTTExportSecretKey"));
+    vblMain->addWidget(unique_ptr<WPushButton> (m_btnApply));
+    
+    m_lePassphrase->keyPressed().connect(m_btnApply, &WPushButton::disable);
+}