Session management

Session Management in MediaWiki

Introduction

Session management is a crucial aspect of developing dynamic and user-friendly web applications built on MediaWiki. It allows you to track user interactions across multiple page requests, maintaining state and providing a personalized experience. Without session management, each HTTP request from a user would be treated as an entirely new request, with no memory of previous interactions. This article provides a comprehensive guide to session management in MediaWiki, targeted at beginners, covering concepts, implementation, security considerations, and best practices. We will explore how to leverage MediaWiki's built-in session handling and extensions to achieve robust and secure session management. Understanding User accounts is fundamental to this topic.

What is a Session?

A session represents a period of interaction between a user and a web application. It begins when a user successfully logs in or initiates a meaningful interaction (like adding an item to a shopping cart, though this is less common in a wiki context, it helps illustrate the concept), and ends when they explicitly log out, or after a period of inactivity.

Key characteristics of a session:

**Stateful:** Unlike stateless HTTP requests, sessions maintain information about the user across multiple requests.
**Unique Identifier:** Each session is assigned a unique identifier, typically stored in a cookie on the user’s browser.
**Server-Side Storage:** Session data is generally stored on the server, ensuring security and preventing manipulation by the user.
**Time-Limited:** Sessions have a defined lifespan, either based on inactivity or a fixed duration.

In the context of MediaWiki, a session helps maintain user login status, track preferences, store temporary data related to editing or viewing pages, and potentially manage workflows within extensions.

How Sessions Work in MediaWiki

MediaWiki, built upon the PHP scripting language, leverages PHP's native session management capabilities. However, it adds its own layers of abstraction and configuration to integrate session handling seamlessly with the wiki's framework.

1. **Session Start:** When a user accesses a MediaWiki page, the wiki’s core PHP code typically initiates a session using `session_start()`. This function (or its equivalent within the MediaWiki environment) attempts to retrieve an existing session ID from a cookie sent by the user's browser.

2. **Session ID:** If a session ID is found, the server retrieves the corresponding session data from its storage. If no session ID is present, a new session is created, a unique ID is generated, and the ID is sent to the user's browser as a cookie. The session ID is usually stored in a cookie named `mwSession`. The security of this cookie is paramount, as it's the key to hijacking a user's session. Consider enabling HTTPS for all wiki traffic.

3. **Session Data:** Session data is stored in key-value pairs on the server. This data can include user ID, login status, preferences, temporary variables, and any other information needed to maintain the user's context throughout their interaction with the wiki. MediaWiki utilizes the `$wgSession` global variable for accessing and manipulating session data.

4. **Session Storage:** By default, PHP stores session data in temporary files on the server. However, MediaWiki allows administrators to configure different session storage mechanisms, such as database-backed sessions (using MySQL, PostgreSQL, or other supported databases) or even external caching systems like Memcached or Redis. Database sessions generally offer better performance and scalability for high-traffic wikis. See Configuration for details on modifying session storage.

5. **Session End:** A session ends when the user logs out (explicitly terminating the session), the session cookie expires, or the server explicitly destroys the session. MediaWiki provides functions for logging users out and destroying their sessions.

Accessing and Manipulating Session Data

MediaWiki provides several ways to access and manipulate session data. The primary method is through the `$wgSession` global variable.

**Setting Session Variables:** To store data in the session, use the following syntax:

```php global $wgSession; $wgSession->set( 'username', 'JohnDoe' ); $wgSession->set( 'preferredLanguage', 'en' ); ```

**Retrieving Session Variables:** To retrieve data from the session, use:

```php global $wgSession; $username = $wgSession->get( 'username' ); $preferredLanguage = $wgSession->get( 'preferredLanguage' ); ```

**Checking if a Session Variable Exists:**

```php global $wgSession; if ( $wgSession->has( 'username' ) ) {

   $username = $wgSession->get( 'username' );

} ```

**Deleting Session Variables:**

```php global $wgSession; $wgSession->remove( 'username' ); ```

**Destroying the Entire Session:** While generally handled by logout functions, you can explicitly destroy the session:

```php global $wgSession; $wgSession->destroy(); ```

These functions provide a simple and consistent interface for managing session data within MediaWiki extensions and custom code. Remember to always sanitize and validate any data retrieved from the session before using it in your application, to prevent security vulnerabilities. See Security for more details. Understanding Hooks can allow you to intercept and modify session data.

Configuration Options

MediaWiki offers several configuration options that control session behavior. These options are typically set in the `LocalSettings.php` file.

**`$wgSessionCacheType`:** Specifies the type of session cache to use. Common options include:

   * `'file'`: (Default) Uses temporary files for session storage.
   * `'database'`: Stores session data in the MediaWiki database. This is recommended for high-traffic wikis.
   * `'memcached'`: Uses Memcached for session storage.
   * `'redis'`: Uses Redis for session storage.

**`$wgSessionCacheStorage`:** Specifies the database table or Memcached/Redis server details to use when `$wgSessionCacheType` is set to `'database'`, `'memcached'`, or `'redis'`.

**`$wgSessionExpiryInterval`:** Sets the session expiry time in seconds. The default is typically 28800 seconds (8 hours). Adjust this value based on your wiki's security requirements and user expectations.

**`$wgSessionName`:** Defines the name of the session cookie. The default is `'mwSession'`. Changing this can add a small layer of obscurity, but is not a primary security measure.

**`$wgSessionHttpOnly`:** If set to `true`, forces the session cookie to be marked as HTTPOnly, preventing client-side scripts from accessing it. This mitigates the risk of cross-site scripting (XSS) attacks. **Highly recommended.**

**`$wgSessionSecure`:** If set to `true`, forces the session cookie to be transmitted only over HTTPS. **Highly recommended.**

**`$wgSessionSameSite`:** Controls the SameSite attribute of the session cookie, providing protection against Cross-Site Request Forgery (CSRF) attacks. Options include `Lax`, `Strict`, and `None`. `None` requires `$wgSessionSecure` to be set to `true`.

Proper configuration of these options is crucial for ensuring both the security and performance of your MediaWiki installation. Consult the Manual:Configuration for a complete list of available session-related configuration options.

Security Considerations

Session management is a critical area for security. A compromised session can allow an attacker to impersonate a legitimate user and gain unauthorized access to sensitive information.

**HTTPS:** Always use HTTPS to encrypt all communication between the user's browser and the wiki server. This prevents attackers from intercepting the session ID cookie.

**HTTPOnly Cookie:** Set the `$wgSessionHttpOnly` configuration option to `true` to prevent client-side scripts from accessing the session cookie. This mitigates the risk of XSS attacks.

**Secure Cookie:** Set the `$wgSessionSecure` configuration option to `true` to ensure that the session cookie is only transmitted over HTTPS.

**SameSite Cookie:** Use the `$wgSessionSameSite` configuration option to protect against CSRF attacks. `Lax` is generally a good default choice, but `Strict` may be appropriate for more sensitive applications.

**Session Expiration:** Set a reasonable session expiration time to limit the window of opportunity for an attacker to use a stolen session ID. Consider shorter expiration times for highly sensitive applications.

**Session Regeneration:** Regenerate the session ID after a user logs in or performs a sensitive action. This prevents session fixation attacks. MediaWiki's login system generally handles session regeneration automatically.

**Input Validation:** Always validate and sanitize any data retrieved from the session before using it in your application. This prevents injection attacks.

**Regular Security Audits:** Conduct regular security audits of your MediaWiki installation to identify and address potential vulnerabilities.

**Stay Updated:** Keep your MediaWiki installation and all extensions up to date with the latest security patches.

**Consider Two-Factor Authentication:** Implementing Two-factor authentication adds an extra layer of security, even if a session ID is compromised.

Best Practices

**Minimize Session Data:** Only store essential data in the session. The more data you store, the larger the session size, which can impact performance.

**Use Session Data Sparingly:** Avoid relying on session data for critical business logic. If possible, store data in the database and retrieve it as needed.

**Clear Session Data on Logout:** Explicitly clear all session data when a user logs out.

**Monitor Session Activity:** Monitor session activity for suspicious patterns, such as multiple logins from different locations.

**Error Handling:** Implement robust error handling to gracefully handle session-related errors.

**Understand the limitations:** MediaWiki's session management is designed for basic user authentication and state management. For complex applications, consider using a dedicated session management framework. Consider utilizing API for more complex tasks.

**Test Thoroughly:** Thoroughly test your session management implementation to ensure it is secure and reliable.

Advanced Topics

**Database Sessions:** Implementing database sessions can significantly improve performance and scalability. Requires configuring `$wgSessionCacheType` to `'database'` and providing appropriate database credentials.

**Caching Systems (Memcached/Redis):** Utilizing Memcached or Redis for session storage can further enhance performance, particularly for high-traffic wikis.

**Session Clustering:** For large-scale deployments, consider session clustering to distribute session data across multiple servers, ensuring high availability and scalability. This generally requires external tools and configuration.

**Custom Session Handlers:** You can create custom session handlers to implement specialized session management logic. This requires advanced PHP programming skills and a deep understanding of MediaWiki's internals. See Extension development for more information on creating custom extensions.

Troubleshooting

**Session Not Starting:** Check your PHP configuration to ensure that session support is enabled. Verify that the session save path is writable. Review the MediaWiki error logs for any session-related errors.

**Session Data Not Persisting:** Verify that the session cookie is being sent and received correctly by the browser. Check the session storage configuration to ensure that session data is being saved properly.

**Session Hijacking:** Implement the security measures described above, such as HTTPS, HTTPOnly cookies, and session regeneration.

**Performance Issues:** Optimize your session storage configuration. Consider using a database or caching system for session storage. Minimize the amount of data stored in the session.

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