1️⃣ RESTful API Development

🔹 What is REST API?

REST (Representational State Transfer) is a way to build APIs using HTTP methods.

🔹 HTTP Methods:

• GET → Fetch data
• POST → Create data
• PUT/PATCH → Update data
• DELETE → Remove data

🔹 Example (Simple PHP API)

<?php
header("Content-Type: application/json");$data = [
    ["id" => 1, "name" => "Aditya"],
    ["id" => 2, "name" => "Rahul"]
];echo json_encode($data);

🔹 API Routing (Basic)

$request = $_SERVER['REQUEST_METHOD'];if ($request == 'GET') {
    echo "Fetching data";
} elseif ($request == 'POST') {
    echo "Creating data";
}

🔹 Best Practices:

• Use JSON format
• Proper HTTP status codes (200, 404, 500)
• Secure endpoints
• Version your API (/api/v1/)

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2️⃣ Authentication (JWT & Sessions)

🔹 Session Authentication

• Stores user data on server
• Uses cookies

session_start();$_SESSION['user'] = "Aditya";if(isset($_SESSION['user'])){
    echo "Logged in as " . $_SESSION['user'];
}

🔹 JWT (JSON Web Token)

Stateless authentication (no session stored on server)

🔹 JWT Flow:

1. User logs in
2. Server generates token
3. Client stores token
4. Token sent in headers for every request

🔹 Example (Concept)

$token = base64_encode(json_encode(["user_id" => 1]));
echo $token;

🔹 Real JWT uses:

• Signature
• Secret key
• Expiry time

Libraries:

• firebase/php-jwt

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3️⃣ Middleware

🔹 What is Middleware?

Middleware acts as a filter before request reaches main logic.

🔹 Use Cases:

• Authentication check
• Logging
• Rate limiting

🔹 Example

function authMiddleware() {
    if(!isset($_SESSION['user'])) {
        die("Unauthorized");
    }
}

Usage:

authMiddleware();
echo "Protected Content";

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4️⃣ Dependency Injection (DI)

🔹 What is DI?

Instead of creating objects inside a class, you pass them from outside.

❌ Without DI

class User {
    public function __construct() {
        $this->db = new Database();
    }
}

✅ With DI

class User {
    private $db;    public function __construct($db) {
        $this->db = $db;
    }
}$db = new Database();
$user = new User($db);

🔹 Benefits:

• Easy testing
• Loose coupling
• Better code structure

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🚀 Pro Tips (Important for Students & Developers)

• Use MVC framework (Laravel) for real projects
• Always validate & sanitize input
• Secure APIs with JWT + HTTPS
• Use Postman for API testing
• Follow PSR standards