This guide shows how to implement email magic link for MFA. You can follow the same approach for step-up auth or adaptive MFA.
  1. Navigate to the Authenticators section and click Setup Email magic link.
  2. Choose and set up an email provider you want to use in the next screen. You can choose Authsignal for development purposes, but it’s recommended not to use it in production. Then click Activate Email Magic Link.
Email magic link setup

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Grab your Authsignal credentials

Head to Settings and grab your Tenant ID, API URL and API secret key. Add them as environment variables in your project: 
AUTHSIGNAL_API_URL=your_region_api_url
AUTHSIGNAL_TENANT_ID=your_tenant_id
AUTHSIGNAL_SECRET_KEY=your_secret_key

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Implementation

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1. Backend - Track an action

When a user performs an action that requires authentication, your backend should track the action. You can use our Server SDK or Server API to track the action. The code snippets in this guide references the SDKs. 
import { Authsignal } from '@authsignal/node';

const authsignal = new Authsignal({
  apiSecretKey: process.env.AUTHSIGNAL_SECRET_KEY,
});

// Track the sign-in action
const trackResponse = await authsignal.track({
  userId: 'dc58c6dc-a1fd-4a4f-8e2f-846636dd4833',
  action: 'signIn',
  attributes: { email }, // Required for email-based auth
});

// Handle different action outcomes
if (trackResponse.state === 'CHALLENGE_REQUIRED') {
  // User needs to complete email-based challenge
  return { token: trackResponse.token };
} else if (trackResponse.state === 'ALLOW') {
  // Proceed with the action - no challenge needed
  return { success: true };
} else if (trackResponse.state === 'BLOCK') {
  // Block the action for security reasons
  return { error: 'Action blocked for security reasons' };
}
Understanding action statesWhen you track an action, Authsignal returns one of four possible states:
  • CHALLENGE_REQUIRED - User must complete an authentication challenge (proceed to step 2)
  • ALLOW - Action is permitted without additional authentication
  • BLOCK - Action is blocked for security reasons
  • REVIEW - Action requires manual review
Learn more about action outcomes.

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2. Frontend - Challenge the user

If the action state is CHALLENGE_REQUIRED, proceed with the magic link challenge using either our Web SDK, Mobile SDKs or Client API. 
import { Authsignal } from '@authsignal/browser';

const authsignal = new Authsignal({
  tenantId: 'YOUR_TENANT_ID',
});

// Set the token from the track response
authsignal.setToken(token);

// Send the magic link challenge
const challengeResponse = await authsignal.emailML.challenge();

// Check verification status (this will resolve when user clicks the magic link)
const verifyResponse = await authsignal.emailML.checkVerificationStatus();

// Get the verification token to validate on your backend
if (verifyResponse.data?.isVerified) {
  const verificationToken = verifyResponse.data.token;
}

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3. Backend - Validate the challenge

After the user completes the challenge, validate the token on your backend: 
import { Authsignal } from '@authsignal/node';

const authsignal = new Authsignal({
  apiSecretKey: process.env.AUTHSIGNAL_SECRET_KEY,
});

// Validate the verification token
const validationResult = await authsignal.validateChallenge({ token });

if (validationResult.isValid) {
  // Authentication successful - proceed with user session creation
  return { success: true };
}
That’s it! You’ve successfully implemented magic link authentication with Authsignal.

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Next steps

  • Adaptive MFA - Set up smart rules to trigger authentication based on risk
  • Email OTP - Add email-based OTP codes for users who prefer entering codes
  • SMS OTP - Implement SMS-based one-time passwords as an alternative method
  • Passkeys - Offer the most secure and user-friendly passwordless authentication