php auth module

<?php

class credentials
{
    /**
    * PerformLogin
    *
    * Performs the default login proceedure.
    *
    * @param string $username The username of the person logging in.
    * @param string $password The password of the person logging in.
    */
    public static function PerformLogin($username, $password)
    {
        if(!credentials::UsernameExists($username)) {
            return array(
                'success' => false,
                'response' => "Username doesn't exist"
            );
        }

        if(sql::Instance() === false) {
            return array(
                'success' => false,
                'response' => 'SQL connect failure'
            );
        }

        $is_ok = true;

        if($stmt = sql::Prepare("SELECT `id`, `allowed_access`, `password`, `email` FROM `credentials` WHERE `username` = ? LIMIT 1")) {
            $stmt->bind_param('s', $username);
            $is_ok = $stmt->execute();
            $stmt->bind_result($fetch_user_id, $fetch_allowed_access, $fetch_password, $fetch_email);
            $is_ok = $stmt->fetch();
            $stmt->close();
        }
        else {
            $is_ok = false;
        }

        if(!$is_ok) {
            return array(
                'success' => false,
                'response' => 'SQL query failed'
            );
        }

        if(!cryptography::ComparePasswords($password, $fetch_password)) {
            return array(
                'success' => false,
                'response' => 'Invalid password'
            );
        }

        if($fetch_allowed_access === 'false') {
            return array(
                'success' => false,
                'response' => 'No account permissions'
            );
        }

        $session_expiry = strtotime('1month');
        $session_token = cryptography::RandomString(100) . hash('md5', $username . (string)$session_expiry);


        if($stmt = sql::Prepare("INSERT INTO `sessions` (`user_id`, `token`, `expiry`) VALUES (?, ?, ?)")) {
            $stmt->bind_param('isi', $fetch_user_id, $session_token, $session_expiry);
            $is_ok = $stmt->execute();
            $stmt->close();
        }
        else {
            $is_ok = false;
        }

        if($is_ok) {
            return array(
                'success' => true,
                'response' => 'Login successful',
                'session_token' => $session_token,
            );
        }
        else {
            return array(
                'success' => false,
                'response' => 'SQL query failed',
            );
        }
    }

    /**
    * PerformRegistration
    *
    * Performs the default registration proceedure.
    *
    * @param string $username The username of the person registering.
    * @param string $password The password of the person registering.
    * @param string $email The password of the person registering.
    */
    public static function PerformRegistration($username, $password, $email)
    {
        if(strlen($username) < 6) {
            return array(
                'success' => false,
                'response' => 'Username must be atleast 6 characters'
            );
        }

        if(strlen($username) < 6) {
            return array(
                'success' => false,
                'response' => 'Password must be atleast 6 characters'
            );
        }

        if(credentials::UsernameExists($username)) {
            return array(
                'success' => false,
                'response' => 'Username is taken'
            );
        }

        if(credentials::EmailExists($email)) {
            return array(
                'success' => false,
                'response' => 'Email already in use'
            );
        }

        $password = cryptography::HashPassword($password);

        if(sql::Instance() === false) {
            return array(
                'success' => false,
                'response' => 'SQL connect failure'
            );
        }

        if($stmt = sql::Prepare("INSERT INTO `credentials` (`id`, `allowed_access`, `username`, `password`, `email`) VALUES (NULL, 'false', ?, ?, ?)")) {
            $stmt->bind_param('sss', $username, $password, $email);
            $stmt->execute();
            $stmt->close();
        }
        else {
            return array(
                'success' => false,
                'response' => 'SQL prepare failure'
            );
        }


        return array(
            'success' => false,
            'response' => 'Registration successful'
        );
    }

    /**
    * Checks if a username is on the table
    *
    * @param string $username The username you're looking up.
    */
    public static function UsernameExists($username)
    {
        if(sql::Instance() === false) {
            return false;
        }

        if($stmt = sql::Prepare('SELECT COUNT(`id`) FROM `credentials` WHERE `username` = ?')) {
            $stmt->bind_param('s', $username);
            $stmt->execute();
            $stmt->bind_result($fetch_count);
            $stmt->fetch();
            $stmt->close();
        }
        else {
            return false;
        }

        return (isset($fetch_count) ? ($fetch_count > 0) : false);
    }

    /**
    * Checks if a email is on the table
    *
    * @param string $email The email you're looking up.
    */
    public static function EmailExists($email)
    {
        if(sql::Instance() === false) {
            return false;
        }

        if($stmt = sql::Prepare('SELECT COUNT(`id`) FROM `credentials` WHERE `email` = ?')) {
            $stmt->bind_param('s', $email);
            $stmt->execute();
            $stmt->bind_result($fetch_count);
            $stmt->fetch();
            $stmt->close();
        }
        else {
            return false;
        }

        return (isset($fetch_count) ? ($fetch_count > 0) : false);
    }
}