Add Login to Your Svelte Application

  import { writable, derived, get, type Readable } from 'svelte/store';
  import { createAuth0Client, type Auth0Client, type User } from '@auth0/auth0-spa-js';
  import { browser } from '$app/environment';

  export const auth0Client = writable<Auth0Client | null>(null);
  export const user = writable<User | null>(null);
  export const isAuthenticated = writable<boolean>(false);
  export const isLoading = writable<boolean>(true);
  export const error = writable<string | null>(null);

  // Derived stores
  export const isLoggedIn: Readable<boolean> = derived(
    [isAuthenticated, isLoading],
    ([$isAuthenticated, $isLoading]) => $isAuthenticated && !$isLoading
  );

  export async function initializeAuth() {
    if (!browser) return;
    
    try {
      const client = await createAuth0Client({
        domain: import.meta.env.VITE_AUTH0_DOMAIN,
        clientId: import.meta.env.VITE_AUTH0_CLIENT_ID,
        authorizationParams: {
          redirect_uri: window.location.origin
        },
        useRefreshTokens: true,
        cacheLocation: 'localstorage'
      });

      auth0Client.set(client);

      // Handle callback
      if (window.location.search.includes('code=')) {
        await client.handleRedirectCallback();
        window.history.replaceState({}, document.title, window.location.pathname);
      }

      // Check authentication status
      const authenticated = await client.isAuthenticated();
      isAuthenticated.set(authenticated);

      if (authenticated) {
        const userData = await client.getUser();
        user.set(userData || null);
      }

      error.set(null);
    } catch (err) {
      console.error('Auth initialization error:', err);
      error.set(err instanceof Error ? err.message : 'Authentication initialization failed');
    } finally {
      isLoading.set(false);
    }
  }

  export async function login() {
    const client = get(auth0Client);
    if (client) {
      await client.loginWithRedirect();
    }
  }

  export async function logout() {
    const client = get(auth0Client);
    if (client) {
      client.logout({ 
        logoutParams: { 
          returnTo: window.location.origin 
        } 
      });
    }
  }

  export async function getToken(): Promise<string | null> {
    const client = get(auth0Client);
    if (!client) return null;
    
    try {
      return await client.getTokenSilently();
    } catch (err: any) {
      if (err.error === 'login_required') {
        await login();
      }
      return null;
    }
  }