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.h

@@ -0,0 +1,56 @@
+/* 
+ * File:   LoopbackPassphraseProvider.h
+ * Author: SET - nmset@yandex.com
+ * License : GPL v2
+ * Copyright SET - © 2019
+ *
+ * Created on November 2, 2020, 2:57 PM
+ */
+
+#ifndef LOOPBACKPASSPHRASEPROVIDER_H
+#define LOOPBACKPASSPHRASEPROVIDER_H
+
+#include <string>
+#include <gpgme++/interfaces/passphraseprovider.h>
+
+using namespace std;
+
+/**
+ * Replaces default pinentry on a web server.
+ */
+class LoopbackPassphraseProvider : public GpgME::PassphraseProvider
+{
+public:
+    LoopbackPassphraseProvider();
+    LoopbackPassphraseProvider(const string& passphrase);
+    virtual ~LoopbackPassphraseProvider();
+    /**
+     * GPG engine gets its passphrase here.
+     * \n The usefulness of the (out?) parameters needs to be better
+     * understood (by me!).
+     * @param useridHint : Signing keyid | key name | email 
+     * @param description : Signing keyid | Signing keyid | 1 | 0
+     * @param previousWasBad : Always 0, even with bad password
+     * @param canceled : Always 0
+     * @return 
+     */
+    virtual char *getPassphrase(const char *useridHint, const char *description,
+                                bool previousWasBad, bool &canceled);
+    /**
+     * Application must do that.
+     * @param passphrase
+     */
+    void SetPassphrase(const string& passphrase);
+    /**
+     * Application may need it, though it knows what it stored here.
+     * @return 
+     */
+    const string GetPassphrase();
+
+private:
+    char * m_passphrase;
+
+};
+
+#endif /* LOOPBACKPASSPHRASEPROVIDER_H */
+