// check length of $_POST['username']
        if (strlen($_POST['username']) <3){
          echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    The username is too short (requier atleast 3 characters).
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
          ');
          include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
          die();
        }

        // check length of $_POST['password']
        if (strlen($_POST['password']) <5){
          echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Your password is too short (requier atleast 5 characters)!
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
          ');
          include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
          die();
        }
        // Ensure that the user has entered a non-empty username
        if(empty($_POST['username']))
        {
            // Note that die() is generally a terrible way of handling user errors
            // like this.  It is much better to display the error with the form
            // and allow the user to correct their mistake.  However, that is an
            // exercise for you to implement yourself. ;
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Please enter a username.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        // Ensure that the user has entered a non-empty password
        if(empty($_POST['password']))
        {
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Password cant be empty.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        // Make sure the user entered a valid E-Mail address
        // filter_var is a useful PHP function for validating form input, see:
        // http://us.php.net/manual/en/function.filter-var.php
        // http://us.php.net/manual/en/filter.filters.php
        if(!filter_var($_POST['email'], FILTER_VALIDATE_EMAIL))
        {
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Please enter a valid E-mail address.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        // We will use this SQL query to see whether the username entered by the
        // user is already in use.  A SELECT query is used to retrieve data from the database.
        // :username is a special token, we will substitute a real value in its place when
        // we execute the query.
        $query = "
            SELECT
                1
            FROM users
            WHERE
                username = :username
        ";

        // This contains the definitions for any special tokens that we place in
        // our SQL query.  In this case, we are defining a value for the token
        // :username.  It is possible to insert $_POST['username'] directly into
        // your $query string; however doing so is very insecure and opens your
        // code up to SQL injection exploits.  Using tokens prevents this.
        // For more information on SQL injections, see Wikipedia:
        // http://en.wikipedia.org/wiki/SQL_Injection
        $query_params = array(
            ':username' => $_POST['username']
        );

        try
        {
            // These two statements run the query against your database table.
            $stmt = $db->prepare($query);
            $result = $stmt->execute($query_params);
        }
        catch(PDOException $ex)
        {
            // Note: On a production website, you should not output $ex->getMessage().
            // It may provide an attacker with helpful information about your code.
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    We where not able to process your information.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ' . $ex->getMessage());
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        // The fetch() method returns an array representing the "next" row from
        // the selected results, or false if there are no more rows to fetch.
        $row = $stmt->fetch();

        // If a row was returned, then we know a matching username was found in
        // the database already and we should not allow the user to continue.
        if($row)
        {
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Username is already taken
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        // Now we perform the same type of check for the email address, in order
        // to ensure that it is unique.
        $query = "
            SELECT
                1
            FROM users
            WHERE
                email = :email
        ";

        $query_params = array(
            ':email' => $_POST['email']
        );

        try
        {
            $stmt = $db->prepare($query);
            $result = $stmt->execute($query_params);
        }
        catch(PDOException $ex)
        {
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    We where not able to process your information. Please try again.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ' . $ex->getMessage());
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        $row = $stmt->fetch();

        if($row)
        {
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    E-mail address is already taken.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');
              include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
              die();
        }

        // An INSERT query is used to add new rows to a database table.
        // Again, we are using special tokens (technically called parameters) to
        // protect against SQL injection attacks.
        $query = "
            INSERT INTO users (
                username,
                password,
                email
            ) VALUES (
                :username,
                :password,
                :email
            )
        ";


        $password = password_hash($_POST['password']);

        // Here we prepare our tokens for insertion into the SQL query.  We do not
        // store the original password; only the hashed version of it.  We do store
        // the salt (in its plaintext form; this is not a security risk).
        $query_params = array(
            ':username' => $_POST['username'],
            ':password' => $password,
            ':email' => $_POST['email']
        );

        try
        {
            // Execute the query to create the user
            $stmt = $db->prepare($query);
            $result = $stmt->execute($query_params);
        }
        catch(PDOException $ex)
        {
            // Note: On a production website, you should not output $ex->getMessage().
            // It may provide an attacker with helpful information about your code.
            echo('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    We where not able to process your information. Please try again
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ' . $ex->getMessage());
            include $_SERVER["DOCUMENT_ROOT"] . "/assets/php/signup-save.php";
            die();
        }

        ob_clean();
        // This redirects the user back to the login page after they register
        echo'
          <div class="container">
            <div class="flag note note--info">
              <div class="flag__image note__icon">
                <i class="fa fa-info"></i>
              </div>
              <div class="flag__body note__text">
                <p>Successfull!<br />
                We have sent you an E-mail With a verification link. Please use the link to verify your account,
                and complete your registration.</p>
              </div>
              <a href="#" class="note__close">
                <i class="fa fa-times"></i>
              </a>
            </div>
          </div>
        ';

        // Calling die or exit after performing a redirect using the header function
        // is critical.  The rest of your PHP script will continue to execute and
        // will be sent to the user if you do not die or exit.
        die();

    }


//session to store input after die() function
?>

// A salt is randomly generated here to protect again brute force attacks
// and rainbow table attacks.  The following statement generates a hex
// representation of an 8 byte salt.  Representing this in hex provides
// no additional security, but makes it easier for humans to read.
// For more information:
// http://en.wikipedia.org/wiki/Salt_%28cryptography%29
// http://en.wikipedia.org/wiki/Brute-force_attack
// http://en.wikipedia.org/wiki/Rainbow_table
$salt = dechex(mt_rand(0, 2147483647)) . dechex(mt_rand(0, 2147483647));

// This hashes the password with the salt so that it can be stored securely
// in your database.  The output of this next statement is a 64 byte hex
// string representing the 32 byte sha256 hash of the password.  The original
// password cannot be recovered from the hash.  For more information:
// http://en.wikipedia.org/wiki/Cryptographic_hash_function
$password = hash('sha256', $_POST['password'] . $salt);

// Next we hash the hash value 65536 more times.  The purpose of this is to
// protect against brute force attacks.  Now an attacker must compute the hash 65537
// times for each guess they make against a password, whereas if the password
// were hashed only once the attacker would have been able to make 65537 different
// guesses in the same amount of time instead of only one.
for($round = 0; $round < 65536; $round++)
{
    $password = hash('sha256', $password . $salt);
}

// Here we prepare our tokens for insertion into the SQL query.  We do not
// store the original password; only the hashed version of it.  We do store
// the salt (in its plaintext form; this is not a security risk).
$query_params = array(
    ':username' => $_POST['username'],
    ':password' => $password,
    ':salt' => $salt,
    ':email' => $_POST['email']
);

<?php
    // This variable will be used to re-display the user's username to them in the
    // login form if they fail to enter the correct password.  It is initialized here
    // to an empty value, which will be shown if the user has not submitted the form.
    $submitted_username = '';

    // This if statement checks to determine whether the login form has been submitted
    // If it has, then the login code is run, otherwise the form is displayed
    if(!empty($_POST))
    {
        // This query retreives the user's information from the database using
        // their username.
        $query = "
            SELECT
                *
            FROM users
                WHERE
                username = :username
        ";

        // The parameter values
        $query_params = array(
            ':username' => $_POST['username']
        );

        try
        {
            // Execute the query against the database
            $stmt = $db->prepare($query);
            $result = $stmt->execute($query_params);
        }
        catch(PDOException $ex)
        {
            // Note: On a production website, you should not output $ex->getMessage().
            // It may provide an attacker with helpful information about your code.
            die('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    Something went wrong, and we where not able to process your sigin in information.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ' . $ex->getMessage());
        }

        // This variable tells us whether the user has successfully logged in or not.
        // We initialize it to false, assuming they have not.
        // If we determine that they have entered the right details, then we switch it to true.
        $login_ok = false;

        // Retrieve the user data from the database.  If $row is false, then the username
        // they entered is not registered.
        $row = $stmt->fetch();
        if($row)
        {
            // Using the password submitted by the user and the salt stored in the database,
            // we now check to see whether the passwords match by hashing the submitted password
            // and comparing it to the hashed version already stored in the database.
            $check_password = hash('sha256', $_POST['password'] . $row['salt']);
            for($round = 0; $round < 65536; $round++)
            {
                $check_password = hash('sha256', $check_password . $row['salt']);
            }

            if($check_password === $row['password'])
            {
                // If they do, then we flip this to true
                $login_ok = true;
            }
        }

        // If the user logged in successfully, then we send them to the private members-only page
        // Otherwise, we display a login failed message and show the login form again
        if($login_ok)
        {

            // Here I am preparing to store the $row array into the $_SESSION by
            // removing the salt and password values from it.  Although $_SESSION is
            // stored on the server-side, there is no reason to store sensitive values
            // in it unless you have to.  Thus, it is best practice to remove these
            // sensitive values first.
            unset($row['salt']);
            unset($row['password']);

            // This stores the user's data into the session at the index 'user'.
            // We will check this index on the private members-only page to determine whether
            // or not the user is logged in.  We can also use it to retrieve
            // the user's details.
            $_SESSION['user'] = $row;

            $username = htmlentities($_POST['username'], ENT_QUOTES, 'UTF-8');
            $last_life_update = "UPDATE users SET last_seen = now() WHERE username = '$username'";
            $db->query($last_life_update);
            // Redirect the user to the private members-only page.
            ?>

            <!--I use script to redirect instead of PHP because some <meta> tags
            disables the header("Location:"); function. -->
            <script type="text/javascript">document.location.href="/";</script>

            <?php
        }
        else
        {
            // Tell the user they failed
            print('
              <div class="container">
                <div class="flag note note--error">
                  <div class="flag__image note__icon">
                    <i class="fa fa-times"></i>
                  </div>
                  <div class="flag__body note__text">
                    Something went wrong!<br />
                    We where not able to verify your account details, please try again.
                  </div>
                  <a href="#" class="note__close">
                    <i class="fa fa-times"></i>
                  </a>
                </div>
              </div>
                ');

            // Show them their username again so all they have to do is enter a new
            // password.  The use of htmlentities prevents XSS attacks.  You should
            // always use htmlentities on user submitted values before displaying them
            // to any users (including the user that submitted them).  For more information:
            // http://en.wikipedia.org/wiki/XSS_attack
            $submitted_username = htmlentities($_POST['username'], ENT_QUOTES, 'UTF-8');
        }
    }
?>