Signing in users with a custom authentication system

This document shows you how to use Identity Platform to sign in users with a custom authentication system. In custom authentication, you use an authentication server to produce custom signed tokens when a user successfully signs in. Your app receives this token and uses it to authenticate with Identity Platform.

Note: If your app uses a sign-in method that Identity Platform supports (such as email and password), consider migrating users instead of implementing custom authentication.

Before you begin

• Install the client SDK.

• Configure your server to accept user credentials and mint custom tokens.

Signing in users

1. Collect sign-in credentials from the user.

2. Send the credentials to your server. Your server validates the request, and returns a custom JWT.

3. Pass the JWT to signInWithCustomToken() to authenticate the user with Identity Platform:

   Web version 9

   Learn more about the tree-shakeable modular Web API and upgrade from the namespaced API.

   import { getAuth, signInWithCustomToken } from "firebase/auth";
   
   const auth = getAuth();
   signInWithCustomToken(auth, token)
     .then((userCredential) => {
       // Signed in
       const user = userCredential.user;
       // ...
     })
     .catch((error) => {
       const errorCode = error.code;
       const errorMessage = error.message;
       // ...
     });
   auth_sign_in_custom.js

   Web version 8

   firebase.auth().signInWithCustomToken(token)
     .then((userCredential) => {
       // Signed in
       var user = userCredential.user;
       // ...
     })
     .catch((error) => {
       var errorCode = error.code;
       var errorMessage = error.message;
       // ...
     });
   custom.js

What's next

• Configure custom claims on users.
• Use the REST API to integrate Identity Platform with other parts of your custom authentication system.