Add Sign Up functionality to desktop app (#5244)

# Description of Changes
Adds Sign Up with email to desktop app. SSO sign up will come in a
future PR.

frontend/src/desktop/components/SetupWizard/SaaSLoginScreen.tsx

@@ -14,6 +14,7 @@ interface SaaSLoginScreenProps {
   onLogin: (username: string, password: string) => Promise<void>;
   onOAuthSuccess: (userInfo: UserInfo) => Promise<void>;
   onSelfHostedClick: () => void;
+  onSwitchToSignup: () => void;
   loading: boolean;
   error: string | null;
 }
@@ -23,6 +24,7 @@ export const SaaSLoginScreen: React.FC<SaaSLoginScreenProps> = ({
   onLogin,
   onOAuthSuccess,
   onSelfHostedClick,
+  onSwitchToSignup,
   loading,
   error,
 }) => {
@@ -89,6 +91,20 @@ export const SaaSLoginScreen: React.FC<SaaSLoginScreenProps> = ({
         submitButtonText={t('setup.login.submit', 'Login')}
       />
 
+      <div className="navigation-link-container" style={{ marginTop: '0.5rem', textAlign: 'right' }}>
+        <button
+          type="button"
+          onClick={() => {
+            setValidationError(null);
+            onSwitchToSignup();
+          }}
+          className="navigation-link-button"
+          disabled={loading}
+        >
+          {t('signup.signUp', 'Sign Up')}
+        </button>
+      </div>
+
       <SelfHostedLink onClick={onSelfHostedClick} disabled={loading} />
     </>
   );

frontend/src/desktop/components/SetupWizard/SaaSSignupScreen.tsx

@@ -0,0 +1,104 @@
+import React, { useState } from 'react';
+import { useTranslation } from 'react-i18next';
+import LoginHeader from '@app/routes/login/LoginHeader';
+import ErrorMessage from '@app/routes/login/ErrorMessage';
+import SignupForm from '@app/routes/signup/SignupForm';
+import { useSignupFormValidation, SignupFieldErrors } from '@app/routes/signup/SignupFormValidation';
+import { authService } from '@app/services/authService';
+import '@app/routes/authShared/auth.css';
+
+interface SaaSSignupScreenProps {
+  loading: boolean;
+  error: string | null;
+  onLogin: (username: string, password: string) => Promise<void>;
+  onSwitchToLogin: () => void;
+}
+
+export const SaaSSignupScreen: React.FC<SaaSSignupScreenProps> = ({
+  loading,
+  error,
+  onLogin: _onLogin,
+  onSwitchToLogin: _onSwitchToLogin,
+}) => {
+  const { t } = useTranslation();
+  const [email, setEmail] = useState('');
+  const [password, setPassword] = useState('');
+  const [confirmPassword, setConfirmPassword] = useState('');
+  const [validationError, setValidationError] = useState<string | null>(null);
+  const [signupFieldErrors, setSignupFieldErrors] = useState<SignupFieldErrors>({});
+  const [signupSuccessMessage, setSignupSuccessMessage] = useState<string | null>(null);
+  const [isSignupSubmitting, setIsSignupSubmitting] = useState(false);
+  const { validateSignupForm } = useSignupFormValidation();
+
+  const displayError = error || validationError;
+
+  const handleSignupSubmit = async () => {
+    setValidationError(null);
+    setSignupSuccessMessage(null);
+    setSignupFieldErrors({});
+
+    const validation = validateSignupForm(email, password, confirmPassword);
+    if (!validation.isValid) {
+      setValidationError(validation.error);
+      setSignupFieldErrors(validation.fieldErrors || {});
+      return;
+    }
+
+    try {
+      setIsSignupSubmitting(true);
+      await authService.signUpSaas(email.trim(), password);
+      setSignupSuccessMessage(t('signup.checkEmailConfirmation', 'Check your email for a confirmation link to complete your registration.'));
+      setSignupFieldErrors({});
+      setValidationError(null);
+    } catch (err) {
+      setSignupSuccessMessage(null);
+      const message = err instanceof Error ? err.message : t('signup.unexpectedError', { message: 'Unknown error' });
+      setValidationError(message);
+    } finally {
+      setIsSignupSubmitting(false);
+    }
+  };
+
+  return (
+    <>
+      <LoginHeader
+        title={t('signup.title', 'Create an account')}
+        subtitle={t('signup.subtitle', 'Join Stirling PDF')}
+      />
+
+      <ErrorMessage error={displayError} />
+      {signupSuccessMessage && (
+        <div className="success-message">
+          <p className="success-message-text">{signupSuccessMessage}</p>
+        </div>
+      )}
+
+      <SignupForm
+        email={email}
+        password={password}
+        confirmPassword={confirmPassword}
+        setEmail={(value) => {
+          setEmail(value);
+          setValidationError(null);
+          setSignupFieldErrors({});
+        }}
+        setPassword={(value) => {
+          setPassword(value);
+          setValidationError(null);
+          setSignupFieldErrors({});
+        }}
+        setConfirmPassword={(value) => {
+          setConfirmPassword(value);
+          setValidationError(null);
+          setSignupFieldErrors({});
+        }}
+        onSubmit={handleSignupSubmit}
+        isSubmitting={loading || isSignupSubmitting}
+        fieldErrors={signupFieldErrors}
+        showName={false}
+        showTerms={false}
+      />
+
+    </>
+  );
+};

frontend/src/desktop/components/SetupWizard/index.tsx

@@ -2,16 +2,20 @@ import React, { useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { DesktopAuthLayout } from '@app/components/SetupWizard/DesktopAuthLayout';
 import { SaaSLoginScreen } from '@app/components/SetupWizard/SaaSLoginScreen';
+import { SaaSSignupScreen } from '@app/components/SetupWizard/SaaSSignupScreen';
 import { ServerSelectionScreen } from '@app/components/SetupWizard/ServerSelectionScreen';
 import { SelfHostedLoginScreen } from '@app/components/SetupWizard/SelfHostedLoginScreen';
 import { ServerConfig, connectionModeService } from '@app/services/connectionModeService';
 import { authService, UserInfo } from '@app/services/authService';
 import { tauriBackendService } from '@app/services/tauriBackendService';
 import { STIRLING_SAAS_URL } from '@desktop/constants/connection';
+import { listen } from '@tauri-apps/api/event';
+import { useEffect } from 'react';
 import '@app/routes/authShared/auth.css';
 
 enum SetupStep {
   SaaSLogin,
+  SaaSSignup,
   ServerSelection,
   SelfHostedLogin,
 }
@@ -80,6 +84,16 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     setActiveStep(SetupStep.ServerSelection);
   };
 
+  const handleSwitchToSignup = () => {
+    setError(null);
+    setActiveStep(SetupStep.SaaSSignup);
+  };
+
+  const handleSwitchToLogin = () => {
+    setError(null);
+    setActiveStep(SetupStep.SaaSLogin);
+  };
+
   const handleServerSelection = (config: ServerConfig) => {
     setServerConfig(config);
     setError(null);
@@ -128,6 +142,48 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     }
   };
 
+  useEffect(() => {
+    const unsubscribePromise = listen<string>('deep-link', async (event) => {
+      const url = event.payload;
+      if (!url) return;
+
+      try {
+        const parsed = new URL(url);
+
+        // Supabase sends tokens in the URL hash
+        const hash = parsed.hash.replace(/^#/, '');
+        const params = new URLSearchParams(hash);
+        const accessToken = params.get('access_token');
+        const type = params.get('type') || parsed.searchParams.get('type');
+
+        if (!type || (type !== 'signup' && type !== 'recovery' && type !== 'magiclink')) {
+          return;
+        }
+
+        if (!accessToken) {
+          console.error('[SetupWizard] Deep link missing access_token');
+          return;
+        }
+
+        setLoading(true);
+        setError(null);
+
+        await authService.completeSupabaseSession(accessToken, serverConfig?.url || STIRLING_SAAS_URL);
+        await connectionModeService.switchToSaaS(serverConfig?.url || STIRLING_SAAS_URL);
+        tauriBackendService.startBackend().catch(console.error);
+        onComplete();
+      } catch (err) {
+        console.error('[SetupWizard] Failed to handle deep link', err);
+        setError(err instanceof Error ? err.message : 'Failed to complete signup');
+        setLoading(false);
+      }
+    });
+
+    return () => {
+      void unsubscribePromise.then((unsub) => unsub());
+    };
+  }, [onComplete, serverConfig?.url]);
+
   const handleBack = () => {
     setError(null);
     if (activeStep === SetupStep.SelfHostedLogin) {
@@ -135,6 +191,8 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     } else if (activeStep === SetupStep.ServerSelection) {
       setActiveStep(SetupStep.SaaSLogin);
       setServerConfig({ url: STIRLING_SAAS_URL });
+    } else if (activeStep === SetupStep.SaaSSignup) {
+      setActiveStep(SetupStep.SaaSLogin);
     }
   };
 
@@ -147,11 +205,21 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
           onLogin={handleSaaSLogin}
           onOAuthSuccess={handleSaaSLoginOAuth}
           onSelfHostedClick={handleSelfHostedClick}
+          onSwitchToSignup={handleSwitchToSignup}
           loading={loading}
           error={error}
         />
       )}
 
+      {activeStep === SetupStep.SaaSSignup && (
+        <SaaSSignupScreen
+          loading={loading}
+          error={error}
+          onLogin={handleSaaSLogin}
+          onSwitchToLogin={handleSwitchToLogin}
+        />
+      )}
+
       {activeStep === SetupStep.ServerSelection && (
         <ServerSelectionScreen
           onSelect={handleServerSelection}