projectDir

|__src

|  |__@types

|  |  |__fastify

|  |  |  |__index.d.ts

|  |__api

|  |  |__authHook.ts

|__tsconfig.json

declare module 'fastify' {

    export interface FastifyContext<ContextConfig>{

        token: string

    }

}

import {FastifyRequest, FastifyReply} from "fastify";

export default async function authHook(request: FastifyRequest, reply: FastifyReply): Promise<void>{

    // Some logic 

    const token = "example_token" // some result from logic 

    request.context.token = token;

}

{

  "compilerOptions": {

     ...

     "typeRoots": ["src/@types"],

     ...

  }

}

Property 'token' does not exist on type 'FastifyContext<unknown>'.

import { onRequestHookHandler } from "fastify";

declare module "fastify" {

  export interface FastifyRequestContext {

    token: string;

  }

}

const authHook: onRequestHookHandler = async function (request, reply) {

  const token = "example_token";

  request.context.token = token;

};

export default authHook;