This guide shows how to implement email OTP for MFA. You can follow the same approach for step-up auth or adaptive MFA.

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Configure email OTP in the Authsignal Portal

  1. Navigate to the Authenticators section and click Manage Email OTP.
  2. Choose 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 activate the email OTP.

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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 OTP
 }, 
});

// Handle different action outcomes
if (trackResponse.state === 'CHALLENGE_REQUIRED') {
  // User needs to complete email OTP 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 email OTP challenge using either our Browser SDK 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 email OTP challenge
const challengeResponse = await authsignal.email.challenge();

// After user enters the OTP code in your UI
const verifyResponse = await authsignal.email.verify({ 
  code: otpCode 
});

// 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 challenge 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 email OTP authentication with Authsignal.

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Next steps

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