Is it possible to customize the email sent by firebase from sendSignInLinkToEmail

Question

We are implementing Firebase email link login (https://firebase.google.com/docs/auth/web/email-link-auth) and I'd like to customize the mail sent, but it isn't showing up in the list of templates in Firebase. Is it possible to customize this email?

Answer 1

Firebase does not provide a template in the Authentication category by default.

If you would like to send a custom email with the sign in link you will have to use a custom SMTP server and email account. I have created a guide in the past that will work for you here.

You would have to connect to that email account through a library such as nodemailer. Assuming you are using the admin sdk, you should generate the sign in URL through a method such as #generateSignInWithEmailLink. Here is a link to the docs page.

// Admin SDK API to generate the sign in with email link.
const useremail = 'user@example.com';
getAuth()
  .generateSignInWithEmailLink(useremail, actionCodeSettings)
  .then((link) => {
    // Construct sign-in with email link template, embed the link and
    // send using custom SMTP server - this is where you would implement nodemailer or other package
    return sendSignInEmail(useremail, displayName, link);
  })
  .catch((error) => {
    // Some error occurred.
  });

In the past when I've gone through this process it's important to note that the #sendSignInEmail method is just a placeholder Firebase has used for the example. This wasn't very clear to me initially.

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Something to note is that you should not be using the admin sdk in the front end. If you have access to Cloud Functions, create a function that sends this email triggered by a https request from your front end. Ensure that the cloud function checks the authentication of any caller, as by default they are insecure. You could achieve this by passing a user token through as a http variable that is verified inside the Cloud Function using a method such as #verifyIdToken. See the documentation for more details.