如何从我的网站向其他网站发送令牌

I have a token I have generated on my website for a different server to use with their client.

How can I get this token from my website to another website?

Token could look like: 5d41402abc4b2a76b9719d911017c592

PHP (example):

$token = md5(uniqid()); //this is not how my token is actually generated

I was thinking to make my site generate a page and reading that page from another website with iFrame, but now I'm considering the use of cookies.

Does anyone know how I can send this token (cookie or otherwise) to another website?