NestJS Guard + Decorator that allows user access limit to his own resources

self.decorator.ts

import { SetMetadata } from '@nestjs/common';

export interface SelfDecoratorParams {
    userIDParam: string;
    allowAdmins?: boolean;
}

export const Self = (params: SelfDecoratorParams | string) =>
    SetMetadata(
        'selfParams',
        typeof params == 'string' ? { userIDParam: params } : params,
    );

self.guard.ts

import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
import { Observable } from 'rxjs';
import { Reflector } from '@nestjs/core';
import { roles, User } from '../../user.dbentity';
import { SelfDecoratorParams } from '../decorators/self.decorator';

@Injectable()
export class SelfGuard implements CanActivate {
    constructor(private readonly reflector: Reflector) {}

    canActivate(
        context: ExecutionContext,
    ): boolean | Promise<boolean> | Observable<boolean> {
        const request = context.switchToHttp().getRequest();
        const user = request.user as User; //Use passport authentication strategy

        //Priority on method meta
        let selfParams = this.reflector.get<SelfDecoratorParams>(
            'selfParams',
            context.getHandler(),
        );
        if (!selfParams)
            //Check for class meta
            selfParams = this.reflector.get<SelfDecoratorParams>(
                'selfParams',
                context.getClass(),
            );
        //If still no meta, pass
        if (!selfParams) return true;

        let allowAdmins = selfParams.allowAdmins || true;
        let userIDParam = selfParams.userIDParam;

        if (!user) return false;
        if (request.params[userIDParam] == user.id) return true;
        if (allowAdmins && user.role == roles.SUPERUSER) return true;
    }
}

user.controller.ts

import {
    Controller,
    Param,
    Body,
    UseInterceptors,
    Patch,
    UseGuards,
    Req,
} from '@nestjs/common';
import { SelfGuard } from '../authentication/guards/self.guard';
import { Request } from 'express';
import { User } from '../user.dbentity';
import { Self } from '../authentication/decorators/self.decorator';

@Self('id') //here "id" notes that the user id is on the "id" request parameter
@UseGuards(SelfGuard)
@Controller()
export class UserController {
    constructor(service: UserService) {}

    @Get('/sampleResource')
    //You may also use the @Self decorator here for method-specific functionality
    async getSampleResource() {
      return "Sample resource";
    }
    
    
    @Get('/sampleResource-adminCanAccess')
    @Self({userIDParam: 'id', allowAdmins: true})
    async getAdminSampleResource() {
      return "Sample resource";
    }
}