Better PHP Autentication Class [closed]

Authentication and keeping information secure is my goal with writing my Authentication class while making sure it is extendable completely as possible over making it usable for anything over just hashing passwords.

I believe I have made it simple as possible to allow it to hold its own as a class by itself for hashing, generating strings, and making sure that the majority of the data that will be passed through the class is secure as possible.

<?php

/**
 *   Package:  reAuth Class
 *   Authros:  Traven West
 *   Created:  June 2014
**/

/**
 *   Base Authentication Class
 *   Returns, generates, and hashes string values securely with proven 
 *   algorithms and class structure.
**/

class Authentication {

    //  Information for this authentication object
    protected $_data = array();

    //  The object used to generate salts and passwords
    protected $_hashFunction;

    //  Authentication key object
    protected $_authKey = 'PS1eFzMWSGImNOhFfdAliW9maPPm6t4TJBGW31yViVVP9WC0umF6l2F3TOD0kkZj';


    public function __construct() {
      $this->_authKey = $authKey;
      $this->_setupHash() = $hashMethod;

      //  Sets the authentication as sha512/sha256
      $authKey = $hashMethod();

      return $authKey;
    }

    protected function _setupHash() {
        if($this->_hashFunction) {
            return;
        }

        if(extension_loaded('hash')) {
            //  Default hashing algorithm
            $this->_hashFunction = 'sha512';
        }
        else {
            //  Backup option if not sha512 not supported
            $this->_hashFunction = 'sha256';
        }
    }

    //  Perform the generation of the hash based on the function set
    protected function generateHash($data) {
        $this->_setupHash();
        switch($this->_hashFunction) {
            case 'sha512':
                return hash('sha512', $data);
            case 'sha256':
                return hash('sha256', $data);
            default:
                $message = 'Unknown hash type.'
                throw new Exception($message);
        }
    }

}

I strongly believe that SHA512 is supported on all machines now, but I do have to allow the occasion that it may not and revert back to SHA256. Another goal is to create a 64-bit string as the output, if not longer.