A Guide to Injecting Service Inside a Guard in Nest JS

A Guide to Injecting Service Inside a Guard in Nest JS

Have you ever wondered how to inject a service inside a Guard in Nest.js to enhance the security features of your application? It’s a common challenge that developers face when seeking to integrate custom logic with the built-in authorization mechanisms. Injecting services into Guards can significantly expand the functionality and flexibility of your authentication process, enabling you to perform advanced checks and operations before granting access to specific routes.

In this guide, we will delve into the intricacies of injecting services into Guards in Nest.js and explore the benefits it brings to your application’s security architecture.

Injecting Services into Guards in Nest.js

When it comes to injecting a service inside a Guard in Nest.js, you’re likely wondering how to seamlessly integrate your custom logic with the application’s security features. The truth is, injecting services into Guards can be a bit tricky if you don’t know where to start.

To begin with, let’s talk about why we even need to inject services into Guards. In a nutshell, Guards are responsible for authorizing requests and ensuring that only authorized users have access to specific routes or endpoints. However, in some cases, you might need to perform additional checks or operations before allowing a request to proceed.

This is where services come in – they allow you to encapsulate complex logic and reuse it throughout your application.

So, how do you inject a service into a Guard? The answer lies in the `@Inject()` decorator provided by Nest.js. By applying this decorator to your service instance, you can make it available within your Guard.

Here’s an example of how you might inject a service into a Guard:

import { Injectable } from ‘@nestjs/common’;
import { CanActivate } from ‘@nestjs/common’;
import { UsersService } from ‘./users.service’;

export class UserGuard implements CanActivate {
constructor(private readonly usersService: UsersService) {}

async canActivate(context: ExecutionContext): Promise {
const user = await this.usersService.getUserByToken(
if (!user) {
return false;
// Perform additional checks or operations here
return true;

In this example, the `UserGuard` class injects an instance of the `UsersService` using the `@Inject()` decorator. This allows you to access the service’s methods and properties within your Guard.

By injecting services into Guards, you can create more robust and secure authentication mechanisms that are tailored to your specific use case. And, as you continue to develop your application, you’ll find that this approach enables you to reuse code and maintain a high level of flexibility.

Injecting a service inside a Guard in Nest.js opens up a world of possibilities for refining your authentication mechanisms and enforcing stricter security policies. By leveraging the `@Inject()` decorator, you can seamlessly integrate custom logic from services into your Guards, empowering you to perform intricate validations and authorization checks with ease. This approach not only enhances the robustness of your application’s security layers but also promotes code reusability and maintainability.

As you continue to explore the synergy between services and Guards, you’ll discover the power of tailored authentication solutions that adapt to the evolving needs of your application. So, embrace the practice of injecting services into Guards, and watch your Nest.js application’s security framework soar to new heights.


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