Using Fastify preHandler middleware - node.js

Question

Passing a middleware to authenticate user before accessing this route.
When I'm passing tokenController.authUser as a middleware tokenService inside tokenController is undefined. However when I run this method as a function inside the route instead of a middleware it works fine.
server.post('/api/admin/test', { preHandler: [tokenController.authUser] }, async (request: any, reply: any) => {
return null
});
Token Controller :-
import { Users } from "#prisma/client";
import ITokenService from "../../services/tokenService/ITokenService";
import ITokenController from "./ITokenController";
export default class TokenController implements ITokenController {
private readonly tokenService: ITokenService;
constructor(_tokenService: ITokenService) {
this.tokenService = _tokenService;
}
async authUser(request: any, reply: any): Promise<Users | Error> {
const authHeader = request.headers['authorization'];
const token = authHeader && authHeader.split(' ')[1];
if (token === null)
return reply.code(401);
try {
const result = await this.tokenService.verifyToken(token);
console.log(result);
return result;
}
catch (e) {
reply.code(401);
return new Error("Error");
}
}
}
Token Service :-
import { Users } from "#prisma/client";
import ITokenService from "./ITokenService";
export default class TokenService implements ITokenService {
private readonly sign: Function;
private readonly verify: Function;
private readonly secretKey: string;
constructor(sign: Function, verify: Function, _secretKey: string) {
this.sign = sign;
this.verify = verify;
this.secretKey = _secretKey;
}
public async generateToken(user: Users): Promise<string> {
return await this.sign({ user }, this.secretKey);
}
public async verifyToken(token: string): Promise<Users | Error> {
const result = await this.verify(token, this.secretKey);
return result;
}
}

Answer 1

For some reason making a separate middleware function and calling tokenController.authUser inside that method works fine.
const middleware = (_req, _res, next) => {
console.log('middleware');
next()
}
server.post('/api/admin/test', { preHandler: [middleware] }, async (request: any, reply: any) => {
return null
});