Login with email magic links

Magic links can be sent to users by email in order to authenticate existing users.

Note

This implements a backend-to-backend integration for authentication. See Backend Authentication APIs

How it works

Here's an example of a magic link integration. Transmit APIs are shown in pink along with the relevant integration step.

Before you start

Before you start your integration, you'll need a Transmit application. See create an application

Step 1: Sign up users

Before you can login users into your app, they will need to be created in your Transmit tenant and associated with your app. New users can be created using a POST /users request, which must include the user's email address. If the user already exists in your Transmit tenant but isn't yet associated with your app, this request will just add the user to your app (but won't update any other details).

Note
  • You'll need a valid client access token to authorize the request. See Get client access tokens
  • The user's email address will be marked as verified upon their first email-based authentication.

Step 2: Create redirect URI

Create the client-side redirect endpoint that will receive a code when the user clicks the magic link in their email. The redirect URI should accept code as a query parameter. For example, if https://domain.com/verify is your redirect URI, then Transmit will redirect to https://domain.com/verify?code=123abc when the user clicks the link. Your endpoint should pass the code it receives to your backend, where it will be used to obtain user tokens, as described in Step 5.

Step 3: Add redirect URI to app

Add the redirect URI (e.g., https://domain.com/verify) as an allowed redirect URI for your Transmit application. This will also be the redirect_uri that you'll need to pass in the send request. From the Admin Portal under Applications, click on your application to edit its settings and add this URI under Redirect URIs.

Step 4: Send magic links

Use a send request like the one below to send a magic link to the specified email address. The redirect_uri should correspond to the redirect endpoint you created in step 2 and added as a redirect URI in step 3. To customize the email, see Next steps. If the request succeeds, a 200 response is returned.

Note

You'll need a valid client access token to authorize the request. See Get client access tokens

Copy
Copied
import fetch from 'node-fetch';

async function run() {
  const resp = await fetch(
    `https://api.transmitsecurity.io/cis/v1/auth/link/email/send`,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        Authorization: 'Bearer [ACCESS_TOKEN]' // Client access token
      },
      body: JSON.stringify({
        email: '[EMAIL]', // User's email address
        redirect_uri: '[REDIRECT_URI]' // URI that receives a code when the link is clicked
      })
    }
  );

  const data = await resp.json();
  console.log(data);
}

run();

Step 5: Authenticate magic links

When the magic link is clicked, your redirect URI receives a code which your client will then pass to your backend so it can be used to obtain user tokens. Create your backend endpoint that will receive this code and then send a magic link auth request like the one below. If successful, a 200 response will be returned with the user tokens, which should be validated as described here.

Note

You'll need a valid client access token to authorize the request. See Get client access tokens

Copy
Copied
import fetch from 'node-fetch';

async function run() {
  const resp = await fetch(
    `https://api.transmitsecurity.io/cis/v1/auth/link/email/authenticate`,
    {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        Authorization: 'Bearer [ACCESS_TOKEN]' // Client access token
      },
      body: JSON.stringify({
        code: '[CODE]' // Code returned to your client-side redirect endpoint
      })
    }
  );

  const data = await resp.json();
  console.log(data);
}

run();

Here's an example of a successful response:

Copy
Copied
{
  "access_token": "string",
  "id_token": "string",
  "refresh_token": "string",
  "token_type": "string",
  "expires_in": 3600,
  "session_id": "string"
}


Next steps

Once you've completed a basic integration, here are some customizations you can consider:

Email customization

The default email template for Login can be customized either from the Admin Portal or via API (but not both). From the Admin Portal (Authentication > Email magic links), you can customize the color of the button and email address that appear in the message. The email message will use the application's logo and name (see screenshots below for default texts). The subject, text and appearance can also be customized using the email_content object in the send request.

Note

If you pass the email_content object, all the email branding will be taken from there and the default template won't be used at all. This means that if a field is not specified, it will be treated as empty.

Here is a screenshot of the email templates with their customizable field names:

Link settings

From the Admin Portal (Authentication > Email magic links), you can customize settings for the selected app:

  • Expiry time in minutes for the link sent in the email
  • Email sender name ("from" name)

If needed, this expiration time can be overwritten for a specific request using the expiration_time parameter.

Custom email provider

In the Admin Portal (from Settings > Email Provider), you can configure to use your custom email provider (e.g., SMTP or SendGrid) instead of the Transmit default.

Security considerations

To secure your magic link implementation, here are some recommendations.

Guidelines
  • To prevent phishing attacks, ensure that the login is initiated and completed from the same device. Validate that the user agent that requested the link matches the one that redirects to your URI when it's clicked. Use the state parameter in the send request so you can associate it with the callback.
  • Verify the user's email address upon sign up. For example, perform a magic link authentication as part of the onboarding flow (after creating the user in Transmit).
  • To prevent credential harvesting, your backend shouldn't indicate to the client if the user wasn't found.