<?php session_start();

    if( isset( $_POST['Submit'] ) )
    {
        $logins = array('Oliver' => 'teszt','teszt' => '81dc9bdb52d04dc20036dbd8313ed055');

        $Username = isset($_POST['Username']) ? $_POST['Username'] : '';
        $Password = isset($_POST['Password']) ? $_POST['Password'] : '';

        if( isset( $logins[$Username] ) && $logins[$Username] == $Password )
        {
            $_SESSION['UserData']['Username']=$logins[$Username];
            header("location:index.php");
            exit;
        }
        else
        {
            $msg="<span style='color:red'>Invalid Login Details</span>";
        }
    }
?>
<form action="" method="post" name="Login_Form">
  <table width="400" border="0" align="center" cellpadding="5" cellspacing="1" class="Table">
    <?php if(isset($msg)){?>
    <tr>
      <td colspan="2" align="center" valign="top"><?php echo $msg;?></td>
    </tr>
    <?php } ?>
    <tr>
      <td colspan="2" align="left" valign="top"><h3>Login</h3></td>
    </tr>
    <tr>
      <td align="right" valign="top">Username</td>
      <td><input name="Username" type="text" class="Input"></td>
    </tr>
    <tr>
      <td align="right">Password</td>
      <td><input name="Password" type="password" class="Input"></td>
    </tr>
    <tr>
      <td> </td>
      <td><input name="Submit" type="submit" value="Login" class="Button3"></td>
    </tr>
  </table>
</form>