Generating and Validating Signed URLs

Signed URLs carry an expiry and integrity signature so a server can detect tampering.

What It Does

Signed URLs carry an expiry and integrity signature so a server can detect tampering. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Understand the primary operation and its inputs.

<?php
$path = '/download/report/8'; $expires = time() + 300; $secret = 'demo-key';
$signature = hash_hmac('sha256', $path . '|' . $expires, $secret);
echo $signature;

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
$path = '/reports/8'; $expiry = time() + 30; $secret = 'demo-key';
$signature = hash_hmac('sha256', $path . '|' . $expiry, $secret);
$allowed = $expiry >= time() && hash_equals(hash_hmac('sha256', $path . '|' . $expiry, $secret), $signature);
var_dump($allowed);

Practical Example: Putting It to Use

Apply the behavior in a small, controlled scenario.

<?php
$path = '/private/file'; $expiry = time() - 2; $secret = 'demo-key';
$sig = hash_hmac('sha256', $path . '|' . $expiry, $secret);
var_dump($expiry >= time() && hash_equals(hash_hmac('sha256', $path . '|' . $expiry, $secret), $sig));

Important Behavior and Edge Cases

Compare signatures in constant time and authorize the underlying resource; prevent replay if one-time access matters.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• Signed URLs carry an expiry and integrity signature so a server can detect tampering.
• Compare signatures in constant time and authorize the underlying resource; prevent replay if one-time access matters.
• Use hash_hmac() with an application secret and include every security-relevant parameter.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.