Firebase Admin SDK provides the ability to add custom attributes in profile object; with the help of this, we can give user different access control, including role-based controls in the react-firebase app, so they are not designed to store additional data (such as profile and other custom data). We know that this looks like a very convenient way to do so, but it is strongly not recommended, as these claims are stored in the ID token and that impacts the performance issues, because all authenticated requests always contain a Firebase ID token corresponding to the signed in user.

• Custom claims are only for storing the data for controlling user access
• Custom claims are limited in size, so passing a custom claims greater than 1000 bytes will throw an error