Extending User

Internally, LucidAuth defines a BaseUser interface with a standard set of properties:

export interface BaseUser {
  id?: string | null;
  name?: string | null;
  email?: string | null;
  image?: string | null;
  role?: string | null;
}

export interface User extends BaseUser {}

In your application, you might need additional properties available in the user session data. For example, let's say you have added a subscriptionId to your session payload so you can access it via session.user.subscriptionId.

However, if you try to access this property in your code, TypeScript will show an error because subscriptionId is not defined in the default BaseUser interface.

To resolve this, you can use a TypeScript feature called module augmentation. This allows you to "merge" your custom properties into the existing library definition.

In your project root, create a file named lucidauth.d.ts and add the following code:

import "lucidauth/core/types";

declare module "lucidauth/core/types" {
  interface BaseUser {
    subscriptionId?: string;
  }
}

What's happening here?

First, we import the file where the BaseUser type is defined inside the library. Then, we use the declare module syntax to tell TypeScript that we are modifying that specific module.

Inside the module, we re-declare the BaseUser interface with only the new properties. TypeScript automatically merges this definition with the original one inside the library.

Now, BaseUser includes the subscriptionId property, and TypeScript knows it exists. As a result, accessing session.user.subscriptionId in your code will no longer trigger type errors.