WordPress --> Discourse SSO

wordpress-discourse-sso.php

<?php
/**
 * SSO "Page"
 * 
 */
add_action( 'parse_request', 'ac_parse_request' );

function ac_parse_request() {

	// Check for SSO request
	if ( isset( $_GET['request'] ) && $_GET['request'] == 'sso' ) {

		// Variables
		$sso_secret = 'your_sso_secret';
		$discourse_url = 'http://discourse.example.com'; // no trailing slash
		$email = get_option( 'admin_email' );

		//
		// Check if user is logged in to WordPress
		//

		// Not logged in to WordPress, redirect to WordPress login page with redirect back to here
		if ( ! is_user_logged_in() ) {

			// Preserve sso and sig parameters
			$redirect = add_query_arg( '', '' );

			// Change %0A to %0B so it's not stripped out in wp_sanitize_redirect
			$redirect = str_replace( '%0A', '%0B', $redirect );

			// Build login URL
			$login = wp_login_url( $redirect );

			// Redirect to login
			wp_redirect( $login );
			exit;

		}

		// Logged in to WordPress, now try to log in to Discourse with WordPress user information
		else {

			// Payload and signature
			$payload = $_GET['sso'];
			$sig = $_GET['sig'];

			// Change %0B back to %0A
			$payload = urldecode( str_replace( '%0B', '%0A', urlencode( $payload ) ) );

			// Check for helper class
			if ( ! class_exists( 'Discourse_SSO' ) ) {

				// Error message
				echo( 'Helper class is not properly included.' );

				// Terminate
				exit;

			}

			// Validate signature
			$sso = new Discourse_SSO( $sso_secret );

			if ( ! ( $sso->validate( $payload, $sig ) ) ) {

				// Error message
				echo( '<p>Something went wrong. An administrator has been notified and will look into the issue.</p>' );
				
				// Notify administrator
				mail( $email, 'Invalid SSO Request', $current_user->user_login . ' ' . $current_user->user_email );

				// Terminate
				exit;

			}

			// Nonce    
			$nonce = $sso->getNonce( $payload );

			// Current user info
			get_currentuserinfo();

			// Map information
			$params = array(
				'nonce' => $nonce,
				'name' => $current_user->display_name,
				'username' => $current_user->user_login,
				'email' => $current_user->user_email,
				'about_me' => $current_user->description,
				'external_id' => $current_user->ID
			);

			// Build login string
			$q = $sso->buildLoginString( $params );

			// Redirect back to Discourse
			wp_redirect( $discourse_url . '/session/sso_login?' . $q );
			exit;

		}

	}

}