til/next-auth/adjust-the-shape-of-the-user-type.md

Adjust The Shape Of The User Type

Let's say we want extra attributes on our user object that gets passed around as part of authentication with NextAuth.js. If we're using a database adapter, it's because we have added columns to the User table. Or it may be that we are adding extra attributes to the body of the JWT token.

Either way, we need the underlying User type (rather, interface) to reflect that.

Within a declare module block for NextAuth, we can define a User interface with any additional properties that we want.

This adds roles as a required string type.

declare module "next-auth" {
  interface User {
    // ...other properties
    roles: string;
  }
}

Some natural places to add this declaration are in the auth file itself (e.g. src/server/auth.ts). Or we can put it in a dedicated top-level next-auth.d.ts file as long as we tell our tsconfig.json to include it:

{
  ...
  "include": [
    "src/**/*",
    "process.d.ts",
    "next-auth.d.ts"
  ],
  ...
}