Add HTTP auth to perticular file PHP.

add_http_auth.php

<?php
// Http auth start.
$valid_passwords = array( 'bunty' => 'Bunty@123' ); // Key is username and value is password.
$valid_users     = array_keys( $valid_passwords ); // Get all usernames from $valid_passwords array.

$user = $_SERVER['PHP_AUTH_USER'];
$pass = $_SERVER['PHP_AUTH_PW'];

// Check if user is valid.
$validated = ( in_array( $user, $valid_users ) ) && ( $pass == $valid_passwords[ $user ] );

if ( ! $validated ) {
	header( 'WWW-Authenticate: Basic realm="Restricted File"' );
	header( 'HTTP/1.0 401 Unauthorized' );
	die( 'Not authorized' );
}