Magic Links

Note: This is mock/placeholder content for demonstration purposes.

Magic links provide passwordless authentication by sending a one-time link to the user's email.

How It Works

1. User enters their email address
2. System sends an email with a unique link
3. User clicks the link in their email
4. User is automatically signed in

Benefits

• No password to remember - Better UX
• More secure - No password to steal
• Lower friction - Faster sign-up process
• Email verification - Confirms email ownership

Implementation

Magic Link Form

'use client';

import { useForm } from 'react-hook-form';
import { sendMagicLinkAction } from '../_lib/actions';

export function MagicLinkForm() {
  const { register, handleSubmit, formState: { isSubmitting } } = useForm();
  const [sent, setSent] = useState(false);

  const onSubmit = async (data) => {
    const result = await sendMagicLinkAction(data);

    if (result.success) {
      setSent(true);
    }
  };

  if (sent) {
    return (
      <div className="text-center">
        <h2>Check your email</h2>
        <p>We've sent you a magic link to sign in.</p>
      </div>
    );
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <div>
        <label>Email address</label>
        <input
          type="email"
          {...register('email', { required: true })}
          placeholder="you@example.com"
        />
      </div>

      <button type="submit" disabled={isSubmitting}>
        {isSubmitting ? 'Sending...' : 'Send magic link'}
      </button>
    </form>
  );
}

Server Action

'use server';

import { enhanceAction } from '@kit/next/actions';
import { getSupabaseServerClient } from '@kit/supabase/server-client';
import * as z from 'zod';

export const sendMagicLinkAction = enhanceAction(
  async (data) => {
    const client = getSupabaseServerClient();
    const origin = process.env.NEXT_PUBLIC_SITE_URL!;

    const { error } = await client.auth.signInWithOtp({
      email: data.email,
      options: {
        emailRedirectTo: `${origin}/auth/callback`,
        shouldCreateUser: true,
      },
    });

    if (error) throw error;

    return {
      success: true,
      message: 'Check your email for the magic link',
    };
  },
  {
    schema: z.object({
      email: z.string().email(),
    }),
  }
);

Configuration

Enable in Supabase

1. Go to Authentication → Providers → Email
2. Enable "Enable Email Provider"
3. Enable "Enable Email Confirmations"

Configure Email Template

Customize the magic link email in Supabase Dashboard:

1. Go to Authentication → Email Templates
2. Select "Magic Link"
3. Customize the template:

<h2>Sign in to {{ .SiteURL }}</h2>
<p>Click the link below to sign in:</p>
<p><a href="{{ .ConfirmationURL }}">Sign in</a></p>
<p>This link expires in {{ .TokenExpiryHours }} hours.</p>

Callback Handler

Handle the magic link callback:

// app/auth/callback/route.ts
import { createRouteHandlerClient } from '@supabase/auth-helpers-nextjs';
import { cookies } from 'next/headers';
import { NextResponse } from 'next/server';

export async function GET(request: Request) {
  const requestUrl = new URL(request.url);
  const token_hash = requestUrl.searchParams.get('token_hash');
  const type = requestUrl.searchParams.get('type');

  if (token_hash && type === 'magiclink') {
    const cookieStore = cookies();
    const supabase = createRouteHandlerClient({ cookies: () => cookieStore });

    const { error } = await supabase.auth.verifyOtp({
      token_hash,
      type: 'magiclink',
    });

    if (!error) {
      return NextResponse.redirect(new URL('/home', request.url));
    }
  }

  // Return error if verification failed
  return NextResponse.redirect(
    new URL('/auth/sign-in?error=invalid_link', request.url)
  );
}

Advanced Features

Custom Redirect

Specify where users go after clicking the link:

await client.auth.signInWithOtp({
  email: data.email,
  options: {
    emailRedirectTo: `${origin}/onboarding`,
  },
});

Disable Auto Sign-Up

Require users to sign up first:

await client.auth.signInWithOtp({
  email: data.email,
  options: {
    shouldCreateUser: false, // Don't create new users
  },
});

Token Expiry

Configure link expiration (default: 1 hour):

-- In Supabase SQL Editor
ALTER TABLE auth.users
SET default_token_lifetime = '15 minutes';

Rate Limiting

Prevent abuse by rate limiting magic link requests:

import { ratelimit } from '~/lib/rate-limit';

export const sendMagicLinkAction = enhanceAction(
  async (data, user, request) => {
    // Rate limit by IP
    const ip = request.headers.get('x-forwarded-for') || 'unknown';
    const { success } = await ratelimit.limit(ip);

    if (!success) {
      throw new Error('Too many requests. Please try again later.');
    }

    const client = getSupabaseServerClient();

    await client.auth.signInWithOtp({
      email: data.email,
    });

    return { success: true };
  },
  { schema: EmailSchema }
);

Security Considerations

Link Expiration

Magic links should expire quickly:

• Default: 1 hour
• Recommended: 15-30 minutes for production
• Shorter for sensitive actions

One-Time Use

Links should be invalidated after use:

// Supabase handles this automatically
// Each link can only be used once

Email Verification

Ensure emails are verified:

const { data: { user } } = await client.auth.getUser();

if (!user.email_confirmed_at) {
  redirect('/verify-email');
}

User Experience

Loading State

Show feedback while sending:

export function MagicLinkForm() {
  const [status, setStatus] = useState<'idle' | 'sending' | 'sent'>('idle');

  const onSubmit = async (data) => {
    setStatus('sending');
    await sendMagicLinkAction(data);
    setStatus('sent');
  };

  return (
    <>
      {status === 'idle' && <EmailForm onSubmit={onSubmit} />}
      {status === 'sending' && <SendingMessage />}
      {status === 'sent' && <CheckEmailMessage />}
    </>
  );
}

Resend Link

Allow users to request a new link:

export function ResendMagicLink({ email }: { email: string }) {
  const [canResend, setCanResend] = useState(false);
  const [countdown, setCountdown] = useState(60);

  useEffect(() => {
    if (countdown > 0) {
      const timer = setTimeout(() => setCountdown(countdown - 1), 1000);
      return () => clearTimeout(timer);
    } else {
      setCanResend(true);
    }
  }, [countdown]);

  const handleResend = async () => {
    await sendMagicLinkAction({ email });
    setCountdown(60);
    setCanResend(false);
  };

  return (
    <button onClick={handleResend} disabled={!canResend}>
      {canResend ? 'Resend link' : `Resend in ${countdown}s`}
    </button>
  );
}

Email Deliverability

SPF, DKIM, DMARC

Configure email authentication:

1. Add SPF record to DNS
2. Enable DKIM signing
3. Set up DMARC policy

Custom Email Domain

Use your own domain for better deliverability:

1. Go to Project Settings → Auth
2. Configure custom SMTP
3. Verify domain ownership

Monitor Bounces

Track email delivery issues:

// Handle email bounces
export async function handleEmailBounce(email: string) {
  await client.from('email_bounces').insert({
    email,
    bounced_at: new Date(),
  });

  // Notify user via other channel
}

Testing

Local Development

In development, emails go to InBucket:

http://localhost:54324

Check this URL to see magic link emails during testing.

Test Mode

Create a test link without sending email:

if (process.env.NODE_ENV === 'development') {
  console.log('Magic link URL:', confirmationUrl);
}

Best Practices

1. Clear communication - Tell users to check spam
2. Short expiry - 15-30 minutes for security
3. Rate limiting - Prevent abuse
4. Fallback option - Offer password auth as backup
5. Custom domain - Better deliverability
6. Monitor delivery - Track bounces and failures
7. Resend option - Let users request new link
8. Mobile-friendly - Ensure links work on mobile