Allow blank usernames, asking for one at connect time instead

Closes #21. SSH and RDP profiles previously hard-required a username
to even save the profile; that validation is dropped, and
SessionTab::requestConnectOptions() now prompts for it at connect
time when blank, reusing the existing password-prompt bar in
unmasked mode -- the same pattern already used for a blank password.

VNC's username is trickier: most VNC servers never use one (plain VNC
Authentication and no-auth don't), only the two Apple auth schemes
(security types 30/33) do, and which auth method gets used isn't known
until mid-connection, after the server's security-type list has been
negotiated -- too late for the pre-connect prompt SSH/RDP uses. Adds a
new async request/response pair to SessionBackend, usernameRequested()
signal / provideUsername() slot, mirroring the existing SSH host-key-
confirmation pattern. VncSessionBackend pauses its state machine right
before computing an Apple-auth response if no username is available --
without consuming the already-buffered prime/host-key bytes, so
resuming re-parses them identically -- emits the request, and resumes
via provideUsername(). Cancelling (or submitting blank) fails the
connection cleanly instead of sending Apple auth an empty username.

The username is kept on the tab's in-memory profile copy for its
lifetime, not written back to the saved profile, matching how
passwords are already handled.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/PROGRESS.md

@@ -157,6 +157,24 @@ Delivered:
   gets its own prompt, with an empty password allowed through (unlike
   RDP's hard requirement) since some VNC servers are no-auth and there's
   no way to know that before the server's security-type negotiation
+- Profiles can now leave the username blank for every protocol (issue
+  #21): SSH/RDP previously hard-required one at profile-save time; that
+  validation is gone, and `SessionTab` now asks for it at connect time
+  instead (reusing the existing password-prompt bar in unmasked mode),
+  same as it already does for a blank password. VNC's username is only
+  ever asked for if the server's negotiated auth method actually needs
+  one -- plain VNC Authentication and no-auth never do, only the two
+  Apple schemes (30/33) do -- which happens *mid-connection*, after the
+  backend has already picked a security type, not before connecting like
+  SSH/RDP. This needed a new async request/response pair on
+  `SessionBackend` (`usernameRequested()` / `provideUsername()`,
+  mirroring the existing SSH host-key-confirmation pattern):
+  `VncSessionBackend` pauses its state machine mid-parse (without
+  consuming the already-buffered response bytes) and emits the request,
+  resuming once `SessionTab` answers; cancelling fails the connection
+  cleanly rather than sending Apple auth a blank username. The value is
+  kept on the tab's in-memory profile copy for its lifetime, not written
+  back to the saved profile
 - Robustness fix: an unrecognized `FramebufferUpdate` rectangle encoding
   used to abort the connection generically; `kAnnouncedEncodings` is now
   the single source of truth for what `SetEncodings` announces and what

src/profile_dialog.cpp

@@ -257,13 +257,6 @@ void ProfileDialog::accept()
     }
 
     const QString protocol = m_protocolInput->currentText();
-    if ((protocol == QStringLiteral("SSH") || protocol == QStringLiteral("RDP"))
-        && m_usernameInput->text().trimmed().isEmpty()) {
-        QMessageBox::warning(this,
-                             QStringLiteral("Validation Error"),
-                             QStringLiteral("Username is required for %1 profiles.").arg(protocol));
-        return;
-    }
 
     if (protocol == QStringLiteral("SSH")
         && m_authModeInput->currentText() == QStringLiteral("Private Key")) {
@@ -310,12 +303,14 @@ void ProfileDialog::refreshAuthFields()
 
     if (isSsh) {
         m_usernameInput->setPlaceholderText(QStringLiteral("deploy"));
-        m_protocolHint->setText(
+        m_protocolHint->setText(QStringLiteral(
-            QStringLiteral("SSH: username is required. Choose Password or Private Key auth."));
+            "SSH: you'll be asked for a username at connect time if left blank here. "
+            "Choose Password or Private Key auth."));
     } else if (isRdp) {
         m_usernameInput->setPlaceholderText(QStringLiteral("Administrator"));
-        m_protocolHint->setText(
+        m_protocolHint->setText(QStringLiteral(
-            QStringLiteral("RDP: username and password are required. Domain is optional."));
+            "RDP: you'll be asked for a username at connect time if left blank here. "
+            "Domain is optional."));
     } else if (isVnc) {
         m_usernameInput->setPlaceholderText(QStringLiteral("optional"));
         m_protocolHint->setText(QStringLiteral(

src/session_backend.h

@@ -55,6 +55,16 @@ public slots:
     {
         Q_UNUSED(text);
     }
+    // Response to usernameRequested(), for backends that discover mid-
+    // connection (not before connectSession() is even called) that they
+    // need one -- currently only VNC's Apple authentication schemes,
+    // which only require a username for security types 30/33, not for
+    // plain VNC Authentication or no-auth. An empty username is treated
+    // the same as the prompt being cancelled.
+    virtual void provideUsername(const QString& username)
+    {
+        Q_UNUSED(username);
+    }
     virtual void sendKeyEvent(int key,
                               quint32 nativeScanCode,
                               const QString& text,
@@ -93,6 +103,10 @@ signals:
     void connectionError(const QString& displayMessage, const QString& rawMessage);
     void outputReceived(const QString& text);
     void hostKeyConfirmationRequested(const QString& prompt);
+    // Mirrors hostKeyConfirmationRequested()'s request/response shape, for
+    // a backend that discovers mid-connection it needs a username it
+    // wasn't given -- see provideUsername().
+    void usernameRequested(const QString& prompt);
     void frameUpdated(const QImage& frame);
     void remoteDesktopSizeChanged(int width, int height);
     void remoteClipboardTextChanged(const QString& text);

src/session_tab.cpp

@@ -215,6 +215,11 @@ SessionTab::SessionTab(const Profile& profile,
                 m_backend,
                 &SessionBackend::setClipboardText,
                 Qt::QueuedConnection);
+        connect(this,
+                &SessionTab::requestProvideUsername,
+                m_backend,
+                &SessionBackend::provideUsername,
+                Qt::QueuedConnection);
 
         connect(m_backend,
                 &SessionBackend::stateChanged,
@@ -241,6 +246,11 @@ SessionTab::SessionTab(const Profile& profile,
                 this,
                 &SessionTab::onBackendHostKeyConfirmationRequested,
                 Qt::QueuedConnection);
+        connect(m_backend,
+                &SessionBackend::usernameRequested,
+                this,
+                &SessionTab::onBackendUsernameRequested,
+                Qt::QueuedConnection);
         connect(m_backend,
                 &SessionBackend::frameUpdated,
                 this,
@@ -714,6 +724,16 @@ void SessionTab::onBackendHostKeyConfirmationRequested(const QString& prompt)
     emit requestHostKeyConfirmation(reply == QMessageBox::Yes);
 }
 
+void SessionTab::onBackendUsernameRequested(const QString& prompt)
+{
+    showPasswordPrompt(
+        prompt.isEmpty() ? QStringLiteral("Username for %1:").arg(m_profile.host) : prompt,
+        [this](std::optional<QString> username) {
+            emit requestProvideUsername(username.value_or(QString()).trimmed());
+        },
+        false);
+}
+
 void SessionTab::onBackendRemoteClipboardTextChanged(const QString& text)
 {
     if (text == m_lastSyncedClipboardText) {
@@ -983,6 +1003,26 @@ void SessionTab::requestConnectOptions(
     const bool isRdp = m_profile.protocol.compare(QStringLiteral("RDP"), Qt::CaseInsensitive) == 0;
     const bool isVnc = m_profile.protocol.compare(QStringLiteral("VNC"), Qt::CaseInsensitive) == 0;
 
+    // SSH and RDP always need a username; a profile is now allowed to
+    // leave it blank (see profile_dialog.cpp) and get asked here instead,
+    // the same way a blank password is already handled below. The value
+    // is kept on this in-memory m_profile copy for the rest of the tab's
+    // lifetime, not written back to the saved profile.
+    if ((isSsh || isRdp) && m_profile.username.trimmed().isEmpty()) {
+        showPasswordPrompt(
+            QStringLiteral("%1 username for %2:").arg(m_profile.protocol, m_profile.host),
+            [this, callback](std::optional<QString> username) {
+                if (!username.has_value() || username->trimmed().isEmpty()) {
+                    callback(std::nullopt);
+                    return;
+                }
+                m_profile.username = username->trimmed();
+                requestConnectOptions(callback);
+            },
+            false);
+        return;
+    }
+
     if (isVnc) {
         // Unlike RDP, an empty password is allowed through: some VNC
         // servers (no-auth) don't need one at all, and there's no
@@ -1102,7 +1142,8 @@ void SessionTab::requestConnectOptions(
 }
 
 void SessionTab::showPasswordPrompt(const QString& labelText,
-                                    std::function<void(std::optional<QString>)> callback)
+                                    std::function<void(std::optional<QString>)> callback,
+                                    bool maskInput)
 {
     if (m_passwordPromptCallback) {
         const auto previousCallback = m_passwordPromptCallback;
@@ -1113,6 +1154,7 @@ void SessionTab::showPasswordPrompt(const QString& labelText,
     m_passwordPromptCallback = std::move(callback);
     m_passwordPromptLabel->setText(labelText);
     m_passwordPromptInput->clear();
+    m_passwordPromptInput->setEchoMode(maskInput ? QLineEdit::Password : QLineEdit::Normal);
     m_passwordPromptBar->setVisible(true);
     m_passwordPromptInput->setFocus();
 }

src/session_tab.h

@@ -91,6 +91,7 @@ signals:
     void requestMouseButtonEvent(int x, int y, int button, bool pressed);
     void requestMouseWheelEvent(int x, int y, int deltaX, int deltaY);
     void requestSetClipboardText(const QString& text);
+    void requestProvideUsername(const QString& username);
 
 private slots:
     void onBackendStateChanged(SessionState state, const QString& message);
@@ -98,6 +99,7 @@ private slots:
     void onBackendConnectionError(const QString& displayMessage, const QString& rawMessage);
     void onBackendOutputReceived(const QString& text);
     void onBackendHostKeyConfirmationRequested(const QString& prompt);
+    void onBackendUsernameRequested(const QString& prompt);
     void onBackendRemoteClipboardTextChanged(const QString& text);
     void onSystemClipboardChanged();
 
@@ -149,7 +151,8 @@ private:
     void setupUi();
     void requestConnectOptions(std::function<void(std::optional<SessionConnectOptions>)> callback);
     void showPasswordPrompt(const QString& labelText,
-                            std::function<void(std::optional<QString>)> callback);
+                            std::function<void(std::optional<QString>)> callback,
+                            bool maskInput = true);
     void hidePasswordPrompt();
     bool validateProfileForConnect();
     void appendEvent(const QString& message);

src/vnc_session_backend.cpp

@@ -196,7 +196,8 @@ VncSessionBackend::VncSessionBackend(const Profile& profile, QObject* parent)
       m_tightCompressionMode(0),
       m_tightFilterId(0),
       m_tightLengthByteIndex(0),
-      m_appleAuthKeyLength(0)
+      m_appleAuthKeyLength(0),
+      m_waitingForUsername(false)
 {
     std::memset(m_zrleInflateStream, 0, sizeof(z_stream_s));
     for (z_stream_s* stream : m_tightInflateStreams) {
@@ -531,6 +532,8 @@ void VncSessionBackend::resetProtocolState()
     }
     m_appleAuthGenerator.clear();
     m_appleAuthKeyLength = 0;
+    m_waitingForUsername = false;
+    m_promptedUsername.clear();
 }
 
 bool VncSessionBackend::haveBytes(int count) const
@@ -671,6 +674,47 @@ void VncSessionBackend::sendAppleRsaHostKeyRequest()
     m_socket->write(msg);
 }
 
+QString VncSessionBackend::effectiveUsername() const
+{
+    const QString profileUsername = profile().username.trimmed();
+    return profileUsername.isEmpty() ? m_promptedUsername : profileUsername;
+}
+
+bool VncSessionBackend::ensureUsernameAvailable()
+{
+    if (!effectiveUsername().isEmpty()) {
+        return true;
+    }
+    if (!m_waitingForUsername) {
+        m_waitingForUsername = true;
+        emit usernameRequested(
+            QStringLiteral("A username is required for %1's authentication method:")
+                .arg(profile().host));
+    }
+    return false;
+}
+
+void VncSessionBackend::provideUsername(const QString& username)
+{
+    if (!m_waitingForUsername) {
+        return;
+    }
+    m_waitingForUsername = false;
+    if (m_state != SessionState::Connecting) {
+        // The connection already failed or was torn down while the
+        // prompt was pending -- nothing left to resume.
+        return;
+    }
+    m_promptedUsername = username.trimmed();
+    if (m_promptedUsername.isEmpty()) {
+        failConnection(
+            QStringLiteral("A username is required for this VNC server's authentication method."),
+            QStringLiteral("Username prompt was cancelled or left empty"));
+        return;
+    }
+    processReceiveBuffer();
+}
+
 void VncSessionBackend::finishHandshakeIntoRunningState()
 {
     emit remoteDesktopSizeChanged(m_framebuffer.width(), m_framebuffer.height());
@@ -963,13 +1007,20 @@ void VncSessionBackend::processReceiveBuffer()
             if (!haveBytes(static_cast<int>(m_pendingLength))) {
                 return;
             }
+            // Checked before consuming any bytes: if a username is needed
+            // and not yet available, pause here (leaving m_recvBuffer
+            // untouched) until provideUsername() resumes us and this same
+            // case re-parses identically.
+            if (!ensureUsernameAvailable()) {
+                return;
+            }
             const int keyLength = static_cast<int>(m_appleAuthKeyLength);
             const QByteArray prime = m_recvBuffer.left(keyLength);
             const QByteArray serverPublicKey = m_recvBuffer.mid(keyLength, keyLength);
             m_recvBuffer.remove(0, static_cast<int>(m_pendingLength));
 
             const VncAppleDhAuth::Response response = VncAppleDhAuth::computeResponse(
-                m_appleAuthGenerator, prime, serverPublicKey, profile().username,
+                m_appleAuthGenerator, prime, serverPublicKey, effectiveUsername(),
                 m_activeOptions.password);
             if (response.clientPublicKey.isEmpty()) {
                 failConnection(
@@ -1020,11 +1071,15 @@ void VncSessionBackend::processReceiveBuffer()
             if (!haveBytes(totalBytes)) {
                 return;
             }
+            // See the matching comment in WaitingAppleAuthPrimeAndServerKey.
+            if (!ensureUsernameAvailable()) {
+                return;
+            }
             const QByteArray hostKeyDer = m_recvBuffer.left(static_cast<int>(m_pendingLength));
             m_recvBuffer.remove(0, totalBytes);
 
             const VncAppleRsaAuth::Response response = VncAppleRsaAuth::computeResponse(
-                hostKeyDer, profile().username, m_activeOptions.password);
+                hostKeyDer, effectiveUsername(), m_activeOptions.password);
             if (response.encryptedCredentials.isEmpty() || response.encryptedAesKey.isEmpty()) {
                 failConnection(
                     QStringLiteral(

src/vnc_session_backend.h

@@ -84,6 +84,7 @@ public slots:
     void sendMouseButtonEvent(int x, int y, int button, bool pressed) override;
     void sendMouseWheelEvent(int x, int y, int deltaX, int deltaY) override;
     void setClipboardText(const QString& text) override;
+    void provideUsername(const QString& username) override;
 
 private slots:
     void onSocketConnected();
@@ -209,6 +210,16 @@ private:
     QByteArray m_appleAuthGenerator;
     quint32 m_appleAuthKeyLength;
 
+    // Apple auth (types 30 and 33) is the only case where VNC ever needs a
+    // username -- plain VNC Authentication and no-auth never do, so this
+    // isn't asked for upfront. If profile().username is empty when an
+    // Apple-auth response is about to be computed, processReceiveBuffer()
+    // pauses (leaving the already-buffered bytes untouched so re-entry
+    // re-parses them identically) and emits usernameRequested(); resumed
+    // by provideUsername() once SessionTab answers.
+    bool m_waitingForUsername;
+    QString m_promptedUsername;
+
     void setState(SessionState state, const QString& message);
     void resetProtocolState();
     void processReceiveBuffer();
@@ -227,6 +238,12 @@ private:
     QRect currentHextileTileRect() const;
     void advanceHextileTile();
     bool inflateTightStream(int streamIndex, const QByteArray& compressed, QByteArray* decompressed);
+    QString effectiveUsername() const;
+    // Returns false (and pauses, emitting usernameRequested() at most once
+    // until provideUsername() resumes processing) if a username is needed
+    // but not yet available. Callers must return from processReceiveBuffer()
+    // immediately when this returns false, without consuming any bytes.
+    bool ensureUsernameAvailable();
 };
 
 #endif

tests/test_vnc_session_backend.cpp

@@ -420,6 +420,7 @@ private slots:
     void connectsWithAppleDhAuthenticationRfb38();
     void appleDhAuthIsPreferredOverVncAuthWhenBothOffered();
     void appleDhAuthAcceptsRealCapturedMacOsServerParameters();
+    void cancellingUsernamePromptFailsConnectionCleanly();
 
 private:
     std::unique_ptr<FakeVncServer> m_server;
@@ -2036,8 +2037,20 @@ void TestVncSessionBackend::connectsWithAppleDhAuthenticationRfb38()
         }
     });
 
+    // makeVncProfile() sets no username, and Apple DH is the one VNC auth
+    // method that needs one -- expect the backend to pause and ask,
+    // exactly like a real profile with a blank username would hit at
+    // connect time (see issue #21 / SessionBackend::usernameRequested).
+    QString requestedPrompt;
+    connect(m_backend.get(), &SessionBackend::usernameRequested, this,
+            [this, &requestedPrompt](const QString& prompt) {
+                requestedPrompt = prompt;
+                m_backend->provideUsername(QStringLiteral("tester"));
+            });
+
     m_backend->connectSession(makeOptions(password));
     QTRY_COMPARE(m_lastState, SessionState::Connected);
+    QVERIFY(!requestedPrompt.isEmpty());
 
     // Verify wire order: encrypted credentials (128 bytes) MUST come
     // before the client's public key, per neatvnc's authoritative
@@ -2085,7 +2098,9 @@ void TestVncSessionBackend::connectsWithAppleDhAuthenticationRfb38()
     EVP_CIPHER_CTX_free(decCtx);
 
     QByteArray expected(128, char(0));
+    const QByteArray userBytes = QByteArrayLiteral("tester").left(64);
     const QByteArray passBytes = password.toLatin1().left(64);
+    std::memcpy(expected.data(), userBytes.constData(), static_cast<size_t>(userBytes.size()));
     std::memcpy(expected.data() + 64, passBytes.constData(), static_cast<size_t>(passBytes.size()));
     QCOMPARE(plain, expected);
 
@@ -2172,5 +2187,51 @@ void TestVncSessionBackend::appleDhAuthAcceptsRealCapturedMacOsServerParameters(
     QCOMPARE(response.encryptedCredentials.size(), 128);
 }
 
+void TestVncSessionBackend::cancellingUsernamePromptFailsConnectionCleanly()
+{
+    ToyDhKeypair serverKeypair = generateToyDhKeypair();
+    const QByteArray authMessage = appleDhAuthServerMessage(
+        serverKeypair.generatorBytes, serverKeypair.primeBytes, serverKeypair.publicKeyBytes);
+
+    bool gotUsernameRequest = false;
+    connect(m_backend.get(), &SessionBackend::usernameRequested, this,
+            [this, &gotUsernameRequest](const QString&) {
+                gotUsernameRequest = true;
+                // An empty response mirrors the prompt being cancelled
+                // (see SessionTab::onBackendUsernameRequested).
+                m_backend->provideUsername(QString());
+            });
+
+    connect(m_server.get(), &FakeVncServer::clientConnected, this, [this]() {
+        m_server->sendWhenConnected(QByteArray("RFB 003.008\n"));
+    });
+    connect(m_server.get(), &FakeVncServer::dataReceived, this, [this, authMessage]() {
+        switch (m_server->nextStep()) {
+        case 0: {
+            QByteArray securityTypes;
+            securityTypes.append(char(1));
+            securityTypes.append(char(30)); // Apple's scheme -- no other option offered
+            m_server->sendWhenConnected(securityTypes);
+            break;
+        }
+        case 1:
+            m_server->sendWhenConnected(authMessage);
+            break;
+        default:
+            break;
+        }
+    });
+
+    // No username in the profile (makeVncProfile() sets none) and no
+    // other security type to fall back to.
+    m_backend->connectSession(makeOptions(QStringLiteral("s3cret-pass")));
+    QTRY_COMPARE(m_lastState, SessionState::Failed);
+    QVERIFY(gotUsernameRequest);
+    QVERIFY(m_lastErrorDisplay.contains(QStringLiteral("username"), Qt::CaseInsensitive));
+
+    BN_free(serverKeypair.privateExponent);
+    BN_free(serverKeypair.prime);
+}
+
 QTEST_GUILESS_MAIN(TestVncSessionBackend)
 #include "test_vnc_session_backend.moc"