user Otp Sending and Validation.php

<?php
/**
 * Send Email For OTP
 * Using WP_rand ( because it is cryptographically secure then PHP rand ).
 */
$otp = wp_rand( 100000, 999999 );
$timestemp = current_time('timestamp');
/**
 * OTP stemp Format( TimeStemp:OtpString ) for Ex. 15000000245455:465478
 */
$user_string = current_time('timestamp') .':'. wp_rand( 100000, 999999 );
update_user_meta( $user->ID, 'pass_stemp', $user_string );
$fields = [
    'otp' => $otp,
    'email'=> $user_email,
    'name'=> $user->user_firstname,
];

/** SEND THis to email */
/**
*FOr validation code 
*/
get user meta
?>