`FastifyInterface` TypeScript augmentation when using namespaces

[chiptoma]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Today I used patch-package to patch @fastify/jwt@7.2.4 for the project I'm working on.

When using the namespace option, the fastify.jwt object no longer contains the JWT interface, but the namespace objects.

In my case, I created two namespaces auth and refresh and the fastify.jwt now contains auth: JWT, refresh: JWT.

Unfortunately, I wasn't able to override the augmentation, so I commented it out for the moment.

Maybe this should be left for the implementation to be typed.

Here is the diff that solved my problem:

diff --git a/node_modules/@fastify/jwt/types/jwt.d.ts b/node_modules/@fastify/jwt/types/jwt.d.ts
index d9bc2b4..7d1605b 100644
--- a/node_modules/@fastify/jwt/types/jwt.d.ts
+++ b/node_modules/@fastify/jwt/types/jwt.d.ts
@@ -13,9 +13,11 @@ import {
 } from 'fastify'
 
 declare module 'fastify' {
-  interface FastifyInstance {
-    jwt: fastifyJwt.JWT
-  }
+  // PATCH: If namespaces are used, the `jwt` object will contain the namespaces as a property.
+  // This augmentation prevents later augmentations from overwriting the namespace property.
+  // interface FastifyInstance {
+  //   jwt: fastifyJwt.JWT
+  // }
 
   interface FastifyReply {
     jwtSign(payload: fastifyJwt.SignPayloadType, options?: fastifyJwt.FastifyJwtSignOptions): Promise<string>

This issue body was partially generated by patch-package.

[mcollina]

This is definitely something we would need to fix for Fastify v5 (fastify/fastify#5061)

[piotr-cz]

Here is my workaround when using the 'player' namespace.

I found that FastifyJwtNamespace doesn't augment FastifyRequest and FastifyReply interfaces, but incorrectly FastifyInstance.

import type { FastifyPluginCallback } from 'fastify'
import type { FastifyJWTOptions, FastifyJwtNamespace } from '@fastify/jwt'
import jwt from '@fastify/jwt'

declare module 'fastify' {
  interface FastifyInstance extends FastifyJwtNamespace<{ namespace: 'player' }> {}

  interface FastifyRequest {
    // Custom namespace
    playerJwtVerify: FastifyRequest['jwtVerify'],
    playerJwtDecode: FastifyRequest['jwtDecode'],
  }

  interface FastifyReply {
    // Custon namespace
    playerJwtSign: FastifyReply['jwtSign'],
  }
}

declare module '@fastify/jwt' {
  // Custom Namespace (undocumented)
  interface JWT { player: jwt.JWT }
}

const jwtPlayerPlugin: FastifyPluginCallback = async (fastify) => {
  fastify.register(jwt, {
    namespace: 'player',
  })
})

[hobi9]

I'm having the same issue, it looks like the types are wrong