PHP Code Überprüfung - Secure Code

if($this->userIsLoggedIn)
{
        // DB Logindaten holen und in db_link packen
       require_once("config.php");
       $db_link = mysqli_connect(MYSQL_HOST, MYSQL_BENUTZER, MYSQL_KENNWORT, MYSQL_DATENBANK);
			
        // Variablen 
	date_default_timezone_set("Europe/Berlin");
	$session_id = $this->frontendController->fe_user->id;
	$uid = $this->frontendController->fe_user->user["uid"];
	$username = $this->frontendController->fe_user->user["username"];
	$in_timestamp_unix = time();
	$in_timestamp_date = date("d/m/Y H:i:s");
	$out_timestamp_unix = "";
	$out_timestamp_date = "";
	$active = 1;

        // SQL Statement prepared, da das Session Cookie in jedem Fall gelesen wird (sofern vorhanden), unabhängig vom 
        Inhalt: SQL Injection	
	$stmt = $db_link->prepare('INSERT INTO fe_users_currloggedin(session_id, uid, username, in_timestamp_unix, 
        in_timestamp_date, out_timestamp_unix, out_timestamp_date, active) VALUES(?,?,?,?,?,?,?,?)');
        $stmt->bind_param('sisssssi', $session_id, $uid, $username, $in_timestamp_unix, $in_timestamp_date, 
        $out_timestamp_unix, $out_timestamp_date, $active);
	$stmt->execute();
	$stmt->close();
			
}else
{
        // DB Logindaten holen und in db_link packen
	require_once("config.php");
	$db_link = mysqli_connect(MYSQL_HOST, MYSQL_BENUTZER, MYSQL_KENNWORT, MYSQL_DATENBANK);
  
        // Variablen 
	$session_id = $this->frontendController->fe_user->id;
	$active = 0;
	$out_timestamp_unix = time();
	$out_timestamp_date = date("d/m/Y H:i:s");
	
        // SQL Statement prepared, da das Session Cookie in jedem Fall gelesen wird (sofern vorhanden), unabhängig vom 
        Inhalt: SQL Injection		
	$stmt = $db_link->prepare('UPDATE fe_users_currloggedin SET active=?, out_timestamp_unix=?, 
        out_timestamp_date=? WHERE session_id=?');
	$stmt->bind_param("isss", $active, $out_timestamp_unix, $out_timestamp_date, $session_id);
	$stmt->execute();
	$stmt->close();
}

if(isset($_COOKIE["fe_typo_user"])) // prüfen, ob Cookie gesetzt
{
	$session_id = $_COOKIE["fe_typo_user"]; // Cookie-Value auslesen

        // DB Logindaten holen und in db_link packen
	require_once("config.php");
	$db_link = mysqli_connect(MYSQL_HOST, MYSQL_BENUTZER, MYSQL_KENNWORT, MYSQL_DATENBANK);
      
        // SELECT Abfrage, um Session ID prüfen zu können
	$sql = "SELECT session_id,username,active FROM fe_users_currloggedin";

	$db_erg = mysqli_query($db_link, $sql);
	while ($zeile = mysqli_fetch_array($db_erg))
	{
                // wenn Session ID existiert und active = 1, dann Usernamen aus DB lesen
		if(strcasecmp($zeile["session_id"], $session_id) == 0 && $zeile["active"] == 1)
		{
			$username = $zeile["username"];
			break;
		}
	}
	if(!empty($username)) // prüfen, ob Username-Variable existent (wenn nicht ist DB Abfrage schiefgegangen)
	{
		echo "Successfully logged in.<br>";
		echo "Welcome ".$username;

                // MORE CODE HERE
	}
}
else
{
	echo "You need to login";
}

// DB Logindaten holen und in db_link packen
require_once('config.php');
$db_link = mysqli_connect(MYSQL_HOST, MYSQL_BENUTZER, MYSQL_KENNWORT, MYSQL_DATENBANK);
date_default_timezone_set('Europe/Berlin');
$session_id = $this->frontendController->fe_user->id;

if($this->userIsLoggedIn)
{
    $uid = $this->frontendController->fe_user->user['uid'];
    $username = $this->frontendController->fe_user->user['username'];
    $stmt = $db_link->prepare('INSERT INTO fe_users_currloggedin(session_id, uid, username, in_timestamp_unix,
        in_timestamp_date, out_timestamp_unix, out_timestamp_date, active) VALUES(?,?,?,NOW(),DATE(),"","",1)');
    $stmt->bind_param('sis', $session_id, $uid, $username);
} else {
    $stmt = $db_link->prepare('DELETE fe_users_currloggedin WHERE active=1 AND session_id=?');
    $stmt->bind_param('s', $session_id);
}

$stmt->execute();
$stmt->close();

// DB Logindaten holen und in db_link packen
require_once('config.php');
$db_link = mysqli_connect(MYSQL_HOST, MYSQL_BENUTZER, MYSQL_KENNWORT, MYSQL_DATENBANK);
if(!isset($_COOKIE['fe_typo_user'])) // prüfen, ob Cookie gesetzt
{
    // direkt aussteigen, spart riesige if Verschachtelungen
    // return/exit oder was an dieser Stelle am besten passt (keine Ahnung wie es eingebunden wird)
    return 'You need to login';
}

$session_id = $_COOKIE['fe_typo_user']; // Cookie-Value auslesen
$stmt = $db_link->prepare('SELECT session_id,username,active FROM fe_users_currloggedin WHERE active=1 AND session_id=?');
$stmt->bind_param('s', $session_id);
$stmt->execute();
$result = $stmt->get_result();
$row = $result->fetch_assoc(); // nur das erste ergebnis
$stmt->close();
if(!empty($result))
{
    echo 'Successfully logged in.<br>';
    echo 'Welcome '.$row['username'];
    // MORE CODE HERE
}

<?php

$_GET["a"] = $a = "siudhfiaushfisdf";
var_dump( [
    "int" => (int)$_GET["a"], // korrekt => 0
    "input" => filter_input( INPUT_GET, "a", FILTER_VALIDATE_INT ), // null? 
    "var" => filter_var( $a, FILTER_VALIDATE_INT ) // korrekt => false, Filter nicht gültig
] );

$_GET["a"] = $a = "20";
var_dump( [
    "int" => (int)$_GET["a"], // korrekt => 20
    "input" => filter_input( INPUT_GET, "a", FILTER_VALIDATE_INT ), // null?
    "var" => filter_var( $a, FILTER_VALIDATE_INT ) // korrekt => 20, Filter gültig
] );

$_GET["a"] = $a = 20;
var_dump( [
    "int" => (int)$_GET["a"], // korrekt => 20
    "input" => filter_input( INPUT_GET, "a", FILTER_VALIDATE_INT ), // null?
    "var" => filter_var( $a, FILTER_VALIDATE_INT ) // korrekt => 20, Filter gültig
] );

DELETE FROM fe_users_currloggedin WHERE (lastAction + :timeout) < NOW()

<?php

$arrrr = [
        '12345',
        'b12345',
        '123cdefg',
];

foreach ($arrrr as $val) {
        echo $val. ' int: '.((int)$val).PHP_EOL;
}

$validate_result = (int)$input; 
return $input == $validate_result? $validate_result : $default_value;