To avoid SEO issues on my subdomains, I need to add a "Link" header to support Google's canonical header. The format is as follows (from http://googlewebmastercentral.blogspot.com/2011/06/supporting-relcanonical-http-headers.html):

Link: http://www.example.com/white-paper.html; rel="canonical"

So, the add_header command would need to reference $uri, but it also needs a semi-colon and double quotes. How can I add this header to my config?