Creating Signed URLs in WordPress: Using Nonces and Custom HMAC

Sabuj Kundu 29th Apr 2025

When you need to create temporary or restricted access to content in WordPress, you have two primary options: WordPress nonces and custom signed URLs. This comprehensive guide will show you when and how to use each approach.

This comprehensive blog post combines both techniques with:

1. Clear explanations of both nonces and signed URLs

2. Detailed implementation guides for each method

3. Comparison table highlighting when to use each approach

4. Visual styling for better readability

5. Security best practices for both methods

6. A hybrid approach for cases where both might be needed

7. Practical code examples ready for implementation

The post is structured to help WordPress developers:

• Understand the differences between the approaches

• Implement either solution with confidence

• Choose the right method for their specific use case

• Follow security best practices

Understanding the Options

WordPress Nonces

Nonces (“number used once”) are WordPress’s built-in security mechanism for verifying the intent behind requests. They’re primarily used for:

• CSRF (Cross-Site Request Forgery) protection
• Securing forms and admin actions
• Creating temporary links for authenticated users

Signed URLs

Signed URLs are custom URLs that contain:

• A cryptographic signature
• An expiration timestamp
• Optional access parameters

They’re useful for:

• Sharing private files temporarily
• Granting access to non-WordPress users
• Creating time-limited download links

Comparison Table

Implementing WordPress Nonces

<?php
      // Generate nonce for specific action
      $nonce = wp_create_nonce('view-protected-content');
      
      // Add to URL
      $protected_url = add_query_arg('_wpnonce', $nonce, 
          get_permalink($protected_page_id)
      );
      ?>

<?php
      if (!isset($_GET['_wpnonce']) || 
          !wp_verify_nonce($_GET['_wpnonce'], 'view-protected-content')) {
          wp_die('Security check failed', 'Error', 403);
      }
      // Show protected content
      ?>

<?php
      // Change nonce lifetime to 2 hours
      add_filter('nonce_life', function() {
          return 7200;
      });
      
      // Create nonce for specific user
      $user_id = 123;
      $nonce = wp_create_nonce('user-access-' . $user_id);
      ?>

Implementing Custom Signed URLs

<?php
      function generate_signed_url($base_url, $expires, $secret_key) {
          $url = add_query_arg('expires', $expires, $base_url);
          $signature = hash_hmac('sha256', $url, $secret_key);
          return add_query_arg('signature', $signature, $url);
      }
      
      // Usage:
      $signed_url = generate_signed_url(
          'https://yoursite.com/protected-file.pdf',
          time() + 3600, // 1 hour expiration
          'your-secret-key'
      );
      ?>

<?php
      function validate_signed_url($secret_key) {
          $expires = $_GET['expires'] ?? 0;
          $signature = $_GET['signature'] ?? '';
          
          $request_url = remove_query_arg('signature');
          $request_url = add_query_arg('expires', $expires, $request_url);
          
          if (time() > $expires) return false;
          
          $expected = hash_hmac('sha256', $request_url, $secret_key);
          return hash_equals($signature, $expected);
      }
      
      // Usage:
      if (!validate_signed_url('your-secret-key')) {
          wp_die('Invalid or expired URL', 403);
      }
      ?>

<?php
      // Add IP restriction
      function generate_restricted_url($base_url, $expires, $secret_key) {
          $url = add_query_arg([
              'expires' => $expires,
              'allowed_ip' => $_SERVER['REMOTE_ADDR']
          ], $base_url);
          
          $signature = hash_hmac('sha256', $url, $secret_key);
          return add_query_arg('signature', $signature, $url);
      }
      
      // Validate with IP check
      function validate_restricted_url($secret_key) {
          // ... existing validation ...
          if ($_GET['allowed_ip'] !== $_SERVER['REMOTE_ADDR']) {
              return false;
          }
          return true;
      }
      ?>

When to Use Each Technique

Security Best Practices

Hybrid Approach

For some use cases, you might combine both techniques:

<?php
   // Generate URL with both nonce and signature
   function generate_hybrid_url($user_id, $base_url, $expires, $secret_key) {
       // Add WordPress nonce
       $nonce = wp_create_nonce('hybrid-access-' . $user_id);
       $url = add_query_arg('_wpnonce', $nonce, $base_url);
       
       // Add signed URL parameters
       $url = add_query_arg('expires', $expires, $url);
       $signature = hash_hmac('sha256', $url, $secret_key);
       return add_query_arg('signature', $signature, $url);
   }
   
   // Validate both
   function validate_hybrid_url($user_id, $secret_key) {
       // Verify nonce first
       if (!wp_verify_nonce($_GET['_wpnonce'], 'hybrid-access-' . $user_id)) {
           return false;
       }
       
       // Then verify signature
       return validate_signed_url($secret_key);
   }
   ?>

Conclusion

Both WordPress nonces and custom signed URLs have important roles in WordPress security:

• For WordPress-native functionality (forms, admin actions), nonces are the simpler and more appropriate choice.
• For public-facing, time-limited content sharing, signed URLs provide more flexibility and security.
• For maximum security in critical systems, consider combining both approaches.

By understanding both techniques, you can choose the right tool for each security challenge in your WordPress projects.