Properly type Request type for Authenticated requests and Unauthenticated requests?

Question

Currently I have a declaration file that looks like this:

import { AuthenticatedUser } from ".";

export interface AuthenticatedRequest {
  isAuthenticated: boolean;
  sid: string | null;
  locals: {
    user: AuthenticatedUser | null;
  };
}

declare global {
  namespace Express {
    export interface Request extends AuthenticatedRequest {}
  }
}

I assign these values in my middleware so I know the user will not be able to access certain routes when not authenticated. The problem is I have to do this in every route I have to use my user object:

  if (!req.locals?.user) {
    return res
      .status(StatusCodes.UNAUTHORIZED)
      .json({ message: ReasonPhrases.UNAUTHORIZED });
  }

  const { user } = req.locals;

How can I tell typescript that the user is authenticated for this route? Do I need to have a separate interface and import it into each of these files or is there a more elegant solution?

As always, thanks for your help.

Answer 1

Solved my problem by passing with a payload generic as the first argument and importing into each file (was already doing with regular request type).

import type { AuthenticatedUser } from ".";
import type { Request as ExpressRequest } from "express";

type AuthenticatedRequestPayload = { sid: string; user: AuthenticatedUser };

type UnauthenticatedRequestPayload = {
  sid: string | null;
  user: AuthenticatedUser | null;
};

type PayloadOption = "authenticated" | "unauthenticated";

export type TargetedRequest<Auth = PayloadOption> =
  Auth extends "authenticated"
    ? AuthenticatedRequestPayload
    : UnauthenticatedRequestPayload;

export type Request<
  Auth = PayloadOption,
  P = Record<string, unknown>,
  ResBody = unknown,
  ReqBody = unknown,
  ReqQuery = Record<string, unknown>
> = ExpressRequest<P, ResBody, ReqBody, ReqQuery> & TargetedRequest<Auth>;