Creating a Custom Authentication Flow in Svelte with Supabase

Implementing a custom authentication flow in Svelte using Supabase allows developers to create a seamless and secure login experience tailored to their application’s needs. Supabase provides a powerful backend with real-time capabilities, while Svelte offers a lightweight, reactive frontend framework.

Setting Up Your Environment

Begin by creating a new Svelte project or opening an existing one. Install the Supabase client library using npm:

npm install @supabase/supabase-js

Next, create a Supabase project at supabase.com and obtain your API URL and anon key from the project settings. Store these securely in environment variables or a configuration file.

Initializing Supabase in Svelte

Create a new file, supabaseClient.js, to initialize the client:

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = 'YOUR_SUPABASE_URL';
const supabaseAnonKey = 'YOUR_SUPABASE_ANON_KEY';

export const supabase = createClient(supabaseUrl, supabaseAnonKey);

Designing the Authentication Component

Create a Svelte component, Auth.svelte, to handle user login, registration, and logout functionalities.

<script>
  import { supabase } from './supabaseClient.js';
  import { onMount } from 'svelte';

  let email = '';
  let password = '';
  let user = null;
  let errorMessage = '';

  onMount(async () => {
    const { data: authUser } = await supabase.auth.getUser();
    user = authUser?.user || null;
  });

  async function signIn() {
    const { error } = await supabase.auth.signInWithPassword({ email, password });
    if (error) {
      errorMessage = error.message;
    } else {
      user = supabase.auth.user();
    }
  }

  async function signUp() {
    const { error } = await supabase.auth.signUp({ email, password });
    if (error) {
      errorMessage = error.message;
    } else {
      signIn();
    }
  }

  async function signOut() {
    await supabase.auth.signOut();
    user = null;
  }
</script>

<div>
  {#if user}
    <p>Welcome, {user.email}</p>
    <button on:click={signOut}>Logout</button>
  {:else}
    <input type="email" placeholder="Email" bind:value={email} />
    <input type="password" placeholder="Password" bind:value={password} />
    <button on:click={signIn}>Login</button>
    <button on:click={signUp}>Register</button>
    {#if errorMessage}
      <p style="color:red">{errorMessage}</p>
    {/if}
  {/if}
</div>

Enhancing Security and User Experience

Implement email verification by configuring Supabase’s authentication settings. Use Svelte’s reactive statements to display loading states and success messages. For multi-factor authentication, explore Supabase’s MFA support and integrate it into your flow.

Handling Authentication State

Maintain the user’s authentication state across your app by subscribing to Supabase’s auth state changes:

<script>
  import { supabase } from './supabaseClient.js';

  let user = null;

  supabase.auth.onAuthStateChange((event, session) => {
    user = session?.user || null;
  });
</script>

Conclusion

Creating a custom authentication flow in Svelte with Supabase empowers developers to craft tailored login experiences while leveraging robust backend security. By following these steps, you can build a scalable and secure user authentication system that integrates seamlessly into your Svelte application.

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