Can not access headers in extended Express.Request type

I am trying to extend Express' Request to type exactly what a query will look like. I currently do this as follows:

export interface TypedRequestQuery<T> extends Express.Request {
    query: T;
}

This works for the most part, but some properties do not seem to be defined. For example:

(req as TypedRequestQuery<{data: string}>).headers

Does not work. It results in the following error:

Property 'headers' does not exist on type 'TypedRequestQuery<{ data: string; }>'

I have read in multiple sources that Express.Request is the correct type for a request handler's request argument. But maybe I misunderstood? Leaving out the typings of the request handler does work!:

router.get("/", async (req, res) => {
    req.headers["x-forwarded-for"] // no errors
})

And the headers property is present in the req.

I am using passport.js which I noticed changes the definition of Request (or at least extends it). Not sure if this is the cause.

My question is: Is Express.Request the correct type to be extending from here? If it is, why does the interface seem incomplete and how can I fix this? If not, what type should I extend from?

Express' Request type already lets you define the query type...

export interface Request<
    P = ParamsDictionary,
    ResBody = any,
    ReqBody = any,
    ReqQuery = ParsedQs, // 👈
    Locals extends Record<string, any> = Record<string, any>
> ...

The query type is the 4th generic so you'd need to provide defaults for the first three

import { ParamsDictionary, Request } from "express-serve-static-core";

type TypedRequestQuery<
  TQuery,
  TParams = ParamsDictionary,
  TResBody = any,
  TReqBody = any
> = Request<TParams, TResBody, TReqBody, TQuery>;

Then you can use it in your routes

router.get("/", async (req: TypedRequestQuery<{data: string}>, res) => {
  console.log("headers[x-forwarded-for]:", req.headers["x-forwarded-for"]);
  console.log("query[data]:", req.query.data);

  res.send("I wish Typescript would let us skip generics");
})

Your example fails compilation because you're trying to override the query property with an incompatible type

> none
> error TS2430: Interface 'TypedRequestQuery<T>' incorrectly extends interface 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>'.
> Types of property 'query' are incompatible.
> Type 'T' is not assignable to type 'ParsedQs'.
>
> interface TypedRequestQuery<T> extends Request {
> ~~~~~~~~~~~~~~~~~
>
> interface TypedRequestQuery<T> extends Request {
> ~
> This type parameter might need an `extends ParsedQs` constraint.
>

A compatible version would need to have your query type extend ParsedQs

import { Request } from "express-serve-static-core";
import { ParsedQs } from "qs"

interface TypedRequestQuery<T extends ParsedQs> extends Request {
  query: T;
}