add tryLoadPassphraseUserBackup function to choose between multiple user backups if more exist throw errors

src/cpp/controller/User.cpp

@@ -1,4 +1,5 @@
 #include "User.h"
+#include "UserBackups.h"
 
 #include "sodium.h"
 
@@ -14,6 +15,8 @@
 
 #include "Poco/Timestamp.h"
 
+
+
 namespace controller {
 	User::User(model::table::User* dbModel)
 		: mPassword(nullptr), mGradidoKeyPair(nullptr), mCanDecryptPrivateKey(false), mGradidoCurrentBalance(0)
@@ -227,6 +230,7 @@ namespace controller {
 		return setNewPassword(authenticated_encryption);
 	}
 
+
 	int User::setNewPassword(Poco::AutoPtr<AuthenticatedEncryption> passwd) 
 	{
 		std::unique_lock<std::shared_mutex> _lock(mSharedMutex);
@@ -284,6 +288,26 @@ namespace controller {
 		return result;
 	}
 
+	//! \return -1 no matching entry found
+	//! \return -2 if user id is not set or invalid
+	//! \return  0 matching entry found, load as gradido key pair
+	int User::tryLoadPassphraseUserBackup()
+	{
+		auto user_model = getModel();
+		if (user_model->getID() <= 0) return -2;
+
+		auto backups = UserBackups::load(user_model->getID());
+		if (backups.size() == 0) return -1;
+		for (auto it = backups.begin(); it != backups.end(); it++) {
+			auto key_pair = std::unique_ptr<KeyPairEd25519>((*it)->createGradidoKeyPair());
+			if (key_pair->isTheSame(user_model->getPublicKey())) {
+				setGradidoKeyPair(key_pair.release());
+				return 0;
+			}
+		}
+		return -1;
+	}
+
 
 	int User::checkIfVerificationEmailsShouldBeResend(const Poco::Util::Timer& timer)
 	{

src/cpp/controller/User.h

@@ -37,6 +37,17 @@ namespace controller {
 		// TODO: instead scheduling all, scheduling only for next day and run this function every day (own task for that)
 		static int checkIfVerificationEmailsShouldBeResend(const Poco::Util::Timer& timer);
 
+		//! \brief try to find correct passphrase for this user from db
+		//! 
+		//! select entries from user_backups db table belonging to user
+		//! calculate resulting public key 
+		//! compare with public key from user
+		//! 
+		//! \return -1 no matching entry found
+		//! \return -2 user id invalid or net set
+		//! \return  0 matching entry found, load as gradido key pair
+		int tryLoadPassphraseUserBackup();
+
 		inline size_t load(const std::string& email) { return getModel()->loadFromDB("email", email); }
 		//! \brief try to load user from db via user_id
 		//! \return count of found rows, should be 1 or 0