core-bundle/src/Resources/contao/library/Contao/User.php
public static function triggerImportUserHook($username, $password, $strTable)
	{
		$self = new static();

		if (empty($GLOBALS['TL_HOOKS']['importUser']) || !\is_array($GLOBALS['TL_HOOKS']['importUser']))
		{
			return false;
		}

		@trigger_error('Using the "importUser" hook has been deprecated and will no longer work in Contao 5.0. Use the contao.import_user event instead.', E_USER_DEPRECATED);

		foreach ($GLOBALS['TL_HOOKS']['importUser'] as $callback)
		{
			$self->import($callback[0], 'objImport', true);
			$blnLoaded = $self->objImport->{$callback[1]}($username, $password, $strTable);

			// Load successfull
			if ($blnLoaded === true)
			{
				return true;
			}
		}

		return false;
	}
public static function triggerImportUserHook($username, $password, $strTable)
	{
		$self = new static();

		if (empty($GLOBALS['TL_HOOKS']['importUser']) || !\is_array($GLOBALS['TL_HOOKS']['importUser']))
		{
			return false;
		}

		@trigger_error('Using the "importUser" hook has been deprecated and will no longer work in Contao 5.0. Use the contao.import_user event instead.', E_USER_DEPRECATED);

		foreach ($GLOBALS['TL_HOOKS']['importUser'] as $callback)
		{
			$self->import($callback[0], 'objImport', true);
			$blnLoaded = $self->objImport->{$callback[1]}($username, $password, $strTable);

			// Load successfull
			if ($blnLoaded === true)
			{
				return true;
			}
		}

		return false;
	}
Trigger the importUser hook

@param $username
@param $password
@param $strTable

@return bool|static