Redirect users to the canonical hostname for your site.
var canon = 'my-site.com' 'other-site.com'http
Pass in the request, the response, 1 or more hostnames to accept, and optionally a statusCode to send with the redirect.
If the host arg has
https:// in front of it, then it will be
redirected to https if it's not https already. Likewise if it starts
http:// and is already https.
Returns a function that takes a req/res pair, and which returns true if it redirected, false otherwise.