Login Plugin to another website

Hello,

Does anyone know if there is a plugin or something I can use to create a login page in a page on a wordpress site.

The login form will link to a separate CMS (not wordpress). This has to stay this way as its a custom built CMS with a huge database of information on.

So basically i am creating a wordpress website, then having a “login page” and on this will be a login form which will then launch a new page with access to the other CMS system.

thanks