Merging custom user property into Express Request for keyGenerator

Question

I’m trying to create a keyGenerator function for express-rate-limit that uses user.id as the key:

import rateLimit from 'express-rate-limit';

rateLimit({
  limit: ...,
  windowMs: ...,
  message: ...,
  keyGenerator: (req: Request) => req.user.id, // TS error
})

TS says:

Property 'user' does not exist on type 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>'.

So, I tried extending Request with a custom type:

type AuthRequest = Request & {
  user: {
    id: string
  }
}

rateLimit({
  limit: ...,
  windowMs: ...,
  message: ...,
  keyGenerator: (req: AuthRequest) => req.user.id, // Still error
})

But now I get:

Type '(req: AuthRequest) => string' is not assignable to type 'ValueDeterminingMiddleware<string>'.
Types of parameters 'req' and 'request' are incompatible.
  Type 'Request<...>' is not assignable to type 'AuthRequest'.

How am I supposed to correctly type req.user for my keyGenerator?

Is the import correct? From the docs, it should be: import { rateLimit } from 'express-rate-limit' — Rasul Navir
– Rasul Navir, Commented Sep 23 at 15:30
@Rasul It works either way. We recommend the named import because "naked" imports have a few weird edge cases, but that's not the issue here. — Nathan Friedly
– Nathan Friedly, Commented Oct 17 at 15:52

Nathan Friedly · Accepted Answer · 2025-10-17 15:58:34Z

0

This is just TypeScript being TypeScript. You know that it's an AuthRequest with a .user property added to it, but TypeScript doesn't and express-rate-limit doesn't. Try this:

rateLimit({
  limit: ...,
  windowMs: ...,
  message: ...,
  keyGenerator: (req: Request) => (req as AuthRequest).user.id,
})

answered Oct 17 at 15:58

Nathan Friedly

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