$password = wp_generate_password();
$userdata = array(
      'user_login'   => $email,
      'user_email'   => $email,
      'user_pass'    => $password,
      'display_name' => $firstname . ' ' . $name,
      'first_name'   => $firstname,
      'last_name'    => $name,
      'role'         => 'subscriber',
      'user_registered' => (new DateTime())->format('Y-m-d H:i:s')
);
$user_id = wp_insert_user( $userdata ) ;

// Autologin after registration
wp_set_current_user($user_id);
if (wp_validate_auth_cookie()==FALSE)
{
     wp_set_auth_cookie($user_id, true, false);
}

$response = null;
$current_user = wp_get_current_user();
var_dump( $current_user );

object(WP_User)#3217 (7) {
 ["data"]=>
   object(stdClass)#3218 (0) {
   }
 ["ID"]=>
   int(0)
 ["caps"]=>
   array(0) {
   }
 ["cap_key"]=>
   NULL
 ["roles"]=>
   array(0) {
   }
 ["allcaps"]=>
   array(0) {
   }
 ["filter"]=>
   NULL

/**
 * login_force_update_cookie - Specific action for force overriding the logged_in_cookie
 * when being in the AJAX registration context
 *
 * @param  {type} $logged_in_cookie description
 * @return {type}                   description
 */
public function login_force_update_cookie( $logged_in_cookie ) {
  if ( strstr( $_SERVER['REQUEST_URI'], 'toto/user/register' ) ) {
    $_COOKIE[LOGGED_IN_COOKIE] = $logged_in_cookie;
  }
}

wp_set_current_user($user_id);
if ( wp_validate_auth_cookie( '', 'logged_in' ) != $user_id )
{
   wp_set_auth_cookie( $user_id );
}

// Storing the regitration event for the user
$this->saveLoginEvent( $user_id );
$data = array(
   'user_id' => $user_id,
   'nonce'   => wp_create_nonce( 'wp_rest' ),
   'message' => 'user_created'
);
$response = rest_ensure_response( $data );