Permission callbacks in Wordpress

Introduction

Permission callbacks check if a user can do something before allowing it. This keeps your site safe and controls access.

When creating a custom REST API endpoint and you want only certain users to access it.

When adding a new admin page and you want to restrict it to editors or administrators.

When registering a custom post type and you want to control who can edit or delete those posts.

When building a plugin that needs to check user roles before performing actions.

When you want to prevent unauthorized users from changing settings or data.

Syntax

Wordpress

register_rest_route( 'namespace/v1', '/route', array(
  'methods' => 'GET',
  'callback' => 'your_callback_function',
  'permission_callback' => 'your_permission_function',
));

The permission_callback is a function that returns true if the user can access, or false if not.

If you do not set permission_callback, WordPress will block access by default for security.

Examples

This example allows only users who can edit posts to access the endpoint.

Wordpress

function check_user_permission() {
  return current_user_can('edit_posts');
}

register_rest_route('myplugin/v1', '/data', array(
  'methods' => 'GET',
  'callback' => 'get_data',
  'permission_callback' => 'check_user_permission',
));

This example allows everyone to access the endpoint by always returning true.

Wordpress

register_rest_route('myplugin/v1', '/public', array(
  'methods' => 'GET',
  'callback' => 'public_data',
  'permission_callback' => '__return_true',
));

This example denies access to everyone by always returning false.

Wordpress

function deny_access() {
  return false;
}

register_rest_route('myplugin/v1', '/secret', array(
  'methods' => 'GET',
  'callback' => 'secret_data',
  'permission_callback' => 'deny_access',
));

Sample Program

This code creates a REST API endpoint at /wp-json/myplugin/v1/secret-message. Only users who can manage options (usually admins) can get the secret message. Others get a permission error.

Wordpress

<?php
function myplugin_permission_check() {
  // Only allow users who can manage options (usually admins)
  return current_user_can('manage_options');
}

function myplugin_get_secret_message() {
  return 'This is a secret message for admins only.';
}

add_action('rest_api_init', function () {
  register_rest_route('myplugin/v1', '/secret-message', array(
    'methods' => 'GET',
    'callback' => 'myplugin_get_secret_message',
    'permission_callback' => 'myplugin_permission_check',
  ));
});

Important Notes

Always use permission callbacks to protect your REST API endpoints.

Use WordPress functions like current_user_can() inside your permission callback to check user roles or capabilities.

If your permission callback returns false, WordPress sends a 403 Forbidden error automatically.

Summary

Permission callbacks control who can access REST API routes.

They return true to allow access or false to block it.

Use WordPress capability checks inside permission callbacks for security.

Practice

1. What is the main purpose of a permission callback in WordPress REST API routes?

easy

A. To define the URL of the REST API route

B. To check if the current user has permission to access the route

C. To format the response data before sending

D. To register the REST API route with WordPress

Solution

1. Step 1: Understand permission callback role

   A permission callback is a function that decides if a user can access a REST API route.

2. Step 2: Identify what permission callback checks

   It returns true if the user has the right capability, false otherwise.

3. Final Answer:

   To check if the current user has permission to access the route -> Option B

4. Quick Check:

   Permission callback = access control [OK]

Hint: Permission callbacks control access rights [OK]

Common Mistakes:

• Confusing permission callback with route registration
• Thinking it formats data instead of checking access
• Assuming it sets the route URL

2. Which of the following is the correct way to define a permission callback in register_rest_route?

easy

A. "permission_callback" => array(check_user_permission)

B. "permission_callback" => check_user_permission()

C. "permission_callback" => "check_user_permission()"

D. "permission_callback" => check_user_permission

Solution

1. Step 1: Understand callback syntax in PHP arrays

   Callbacks are passed as callable references without parentheses.

2. Step 2: Identify correct syntax for permission_callback

   It should be a string or callable without calling it immediately, so no parentheses.

3. Final Answer:

   "permission_callback" => check_user_permission -> Option D

4. Quick Check:

   Callback = function name without () [OK]

Hint: Use function name without parentheses for callbacks [OK]

Common Mistakes:

• Adding parentheses calls the function immediately
• Using array() incorrectly for single function
• Passing callback as a string with quotes and parentheses

3. Given this permission callback function, what will register_rest_route allow?

function my_permission_check() {
  return current_user_can('edit_posts');
}

register_rest_route('myplugin/v1', '/data', [
  'methods' => 'GET',
  'callback' => 'my_data_callback',
  'permission_callback' => 'my_permission_check'
]);

medium

A. Only users who can edit posts can access the route

B. All users can access the route

C. No users can access the route

D. Only administrators can access the route

Solution

1. Step 1: Analyze the permission callback function

   The function returns true if the current user has the 'edit_posts' capability.

2. Step 2: Understand effect on route access

   Only users with 'edit_posts' capability can access the route; others get denied.

3. Final Answer:

   Only users who can edit posts can access the route -> Option A

4. Quick Check:

   Capability check controls access [OK]

Hint: Permission callback returns true only for allowed users [OK]

Common Mistakes:

• Assuming all users can access without checking capability
• Confusing 'edit_posts' with administrator only
• Ignoring the return value of permission callback

4. Identify the error in this permission callback code:

function check_permission() {
  if (current_user_can('edit_posts')) {
    return true;
  }
}

medium

A. Function should not return boolean

B. Incorrect capability name used

C. Missing return false when user lacks permission

D. Permission callback must be anonymous function

Solution

1. Step 1: Review function return paths

   The function returns true if user can edit posts, but returns nothing otherwise.

2. Step 2: Understand permission callback requirements

   Permission callbacks must return true or false explicitly to avoid unexpected behavior.

3. Final Answer:

   Missing return false when user lacks permission -> Option C

4. Quick Check:

   Always return true or false in permission callbacks [OK]

Hint: Always return false if permission denied [OK]

Common Mistakes:

• Omitting return false causes implicit null return
• Assuming no return means false automatically
• Using wrong capability names

5. You want to create a REST API route that only allows users who can either edit_posts or publish_posts. Which permission callback function correctly implements this?

hard

A. function permission_check() {
return current_user_can('edit_posts') || current_user_can('publish_posts');
}

B. function permission_check() {
return current_user_can('publish_posts');
}

C. function permission_check() {
if (current_user_can('edit_posts')) {
return true;
}
return false;
}

D. function permission_check() {
return current_user_can('edit_posts') && current_user_can('publish_posts');
}

Solution

1. Step 1: Understand the requirement

   Access should be granted if user can edit posts OR publish posts.

2. Step 2: Analyze each function logic

   function permission_check() { return current_user_can('edit_posts') && current_user_can('publish_posts'); } requires both capabilities (AND), which is too strict. function permission_check() { return current_user_can('edit_posts') || current_user_can('publish_posts'); } uses OR, which matches requirement. function permission_check() { if (current_user_can('edit_posts')) { return true; } return false; } only checks edit_posts. function permission_check() { return current_user_can('publish_posts'); } only checks publish_posts.

3. Final Answer:

   function permission_check() { return current_user_can('edit_posts') || current_user_can('publish_posts'); } -> Option A

4. Quick Check:

   Use OR for either capability allowed [OK]

Hint: Use || to allow either capability [OK]

Common Mistakes:

• Using && instead of || for either/or logic
• Checking only one capability when two are needed
• Not returning false explicitly when needed