Button Shortcode with Post Vars

I need to create a button that links to an external site using a POST method that passes userid, first_name, last_name, email, gender, and site_key (static text). Essentially, the <button>Click</button> will query the database, grab user info, and redirect to a site that is looking for user identification data as shown above.

This seems like a shortcode function, but i’m new to Code Snippets.