Build Authentication Service

Quick Introduction

Build Authentication Service is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only build authentication service — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the E-Commerce Backend. After a user signs in, you need build authentication service working correctly before storing data or showing a dashboard.

Without understanding Build Authentication Service, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• Build Authentication Service is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (E-Commerce Backend) uses build authentication service in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for Build Authentication Service. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

namespace AuthService;

final readonly class TokenPair {
    public function __construct(public string $accessToken, public string $refreshToken, public int $expiresIn) {}
}

final class AuthService {
    public function __construct(private UserRepository $users, private TokenIssuer $issuer) {}

    public function login(string $email, string $password): TokenPair {
        $user = $this->users->findByEmail($email)
            ?? throw new AuthException('Invalid credentials');
        if (!password_verify($password, $user->passwordHash)) {
            throw new AuthException('Invalid credentials');
        }
        return $this->issuer->issue($user->id, ['role' => $user->role]);
    }
}

interface UserRepository { public function findByEmail(string $email): ?User; }
interface TokenIssuer { public function issue(int $userId, array $claims): TokenPair; }
final class AuthException extends \Exception {}

Line by line

1. — part of the build authentication service example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. namespace AuthService; — part of the build authentication service example; run the file to see the result.
4. final readonly class TokenPair { — part of the build authentication service example; run the file to see the result.
5. public function __construct(public string $accessToken, public string $refreshToken, public int $expiresIn) {} — part of the build authentication service example; run the file to see the result.

{"status":"ok"}

Real-World Example

In the E-Commerce Backend, build authentication service appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: Build Authentication Service exercise for E-Commerce Backend