Fix creation of dynamic property warning

includes/classes/Authentication.php

@@ -24,6 +24,62 @@ abstract class Authentication {
 	 */
 	public static $error_message;
 
+	/**
+	 * Site URL
+	 *
+	 * @var string
+	 */
+	public $site_url;
+
+	/**
+	 * Username
+	 *
+	 * @var string
+	 */
+	public $username;
+
+	/**
+	 * Password
+	 *
+	 * @var string
+	 */
+	public $password;
+
+	/**
+	 * API Key
+	 *
+	 * @var string
+	 */
+	public $client_id;
+
+	/**
+	 * API Secret
+	 *
+	 * @var string
+	 */
+	public $client_secret;
+
+	/**
+	 * Redirect URI
+	 *
+	 * @var string
+	 */
+	public $redirect_uri;
+
+	/**
+	 * Access Token
+	 *
+	 * @var string
+	 */
+	public $base64_encoded;
+
+	/**
+	 * Created Post ID
+	 *
+	 * @var string
+	 */
+	public $dt_created_post_id;
+
 	/**
 	 * Set associative arguments as instance variables
 	 *