<?php
$pdo = new PDO( 'mysql:host=127.0.0.1;dbname=app;charset=utf8mb4', 'app', 'example-only', array(
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_EMULATE_PREPARES => false,
) );
$email = filter_input( INPUT_GET, 'email', FILTER_VALIDATE_EMAIL );
if ( ! $email ) { http_response_code( 400 ); exit( 'invalid email' ); }
$stmt = $pdo->prepare( 'SELECT id, display_name FROM users WHERE email = :email LIMIT 1' );
$stmt->execute( array( 'email' => $email ) );
header( 'Content-Type: application/json' );
echo json_encode( $stmt->fetch( PDO::FETCH_ASSOC ) ?: array( 'found' => false ) );