connection.php

<?php
include('common/header.php');
$email = $_GET['email'] ?? '';
$invalid_password = '';
if (isset($_GET['invalid']) && $_GET['invalid'] === 'password'){
  $invalid_password = 'is-invalid';
}
?>
<div class='container d-flex justify-content-center'>
<form method='POST' class="col-md-6" action="private/connectUser.php">
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input name="email" type="email" value="<?php echo $email ?>" class="form-control" id="exampleInputEmail1" aria-describedby="emailHelp" placeholder="Enter email">
  </div>
  <div class="form-group">
    <label for="exampleInputPassword1">Password</label>
    <input name="password" type="password" class="form-control <?php echo $invalid_password; ?>" id="exampleInputPassword1" placeholder="Password">
    <?php if (!empty($invalid_password)){
    ?>
    <div>
        <small id="passwordHelp" class="text-danger">
          Password is incorrect
        </small>      
      </div>
      <?php
    }
    ?>
  </div>

  <button type="submit" class="btn btn-primary">Submit</button>
</form>
</div>
<?php
include('common/footer.php');