Certify key.

In-place editing with a popup if user is allowed in app config file.
User must of course manage at least a private key. User identities of
target key may be selectively chosen. Optionally, certification may be
exportable and non-revocable.

LoopbackPassphraseProvider.cpp

@@ -0,0 +1,59 @@
+/* 
+ * File:   LoopbackPassphraseProvider.cpp
+ * Author: SET - nmset@yandex.com
+ * License : GPL v2
+ * Copyright SET - © 2019
+ * 
+ * Created on November 2, 2020, 2:57 PM
+ */
+
+#include "LoopbackPassphraseProvider.h"
+#include <string.h>
+#include <iostream>
+
+LoopbackPassphraseProvider::LoopbackPassphraseProvider()
+: PassphraseProvider()
+{
+    m_passphrase = strdup("");
+}
+
+LoopbackPassphraseProvider::LoopbackPassphraseProvider(const string& passphrase)
+: PassphraseProvider()
+{
+    m_passphrase = strdup(passphrase.c_str());
+}
+
+LoopbackPassphraseProvider::~LoopbackPassphraseProvider()
+{
+}
+
+/*
+ * Called by GPG engine.
+ * Is not called if gpg-agent already has a valid password.
+ */
+char* LoopbackPassphraseProvider::getPassphrase(const char* useridHint,
+                                                const char* description,
+                                                bool previousWasBad,
+                                                bool& canceled)
+{
+    /*
+    cout << useridHint << endl; // <Signing keyid> <key name> <email>
+    cout << description << endl; // <Signing keyid> <Signing keyid> 1 0
+    cout << previousWasBad << endl; // Always 0, even with bad password
+    cout << canceled << endl; // Always 0
+     */
+    return m_passphrase;
+}
+
+void LoopbackPassphraseProvider::SetPassphrase(const string& passphrase)
+{
+    /*
+     * Memory leak here ?
+     */
+    m_passphrase = strdup(passphrase.c_str());
+}
+
+const string LoopbackPassphraseProvider::GetPassphrase()
+{
+    return m_passphrase;
+}