system/HTTP/RedirectResponse.php
public function with(string $key, $message)
	{
		$session = $this->ensureSession();

		$session->setFlashdata($key, $message);

		return $this;
	}
public function with(string $key, $message)
	{
		$session = $this->ensureSession();

		$session->setFlashdata($key, $message);

		return $this;
	}
Adds a key and message to the session as Flashdata.

@param string       $key
@param string|array $message

@return $this