HTTP::Cookies could maintain consistency in domain name handling while writing vs reading in/from cookie jar

set_cookie() uses the $domain value as it is without changing the casing. But add_cookie_header() calculates the $domain value via _host() which is always lowercase. This creates challenge when we work with case sensitive domain/urls with HTTP::Cookies.

We(@WahidAbdullahK) had a scenario where we had a case sensitive base url (e.g https://sYknjFe.xyz.com) and we had to create a request to a url (e.g https://sYknjFe.xyz.com/data) via LWP::UserAgent with some cookies. So when creating the cookie jar using HTTP::Cookies we just passed the domain name that we got out of base url which is sYknjFe.xyz.com and set_cookie() added as it is and the created cookie jar is then passed to LWP::UserAgent object for raising a http request. While raising the http request with the url value https://sYknjFe.xyz.com/data add_cookie_header() of HTTP::Cookies got invoked but now it was looking for the lower cased domain(from _host()) in cookie jar i.e syknjfe.xyz.com and because of case difference it doesn't find it and end up in not adding any of the cookies in the http header. Though I could see some references in the web that urls & cookie domain paths can be case sensitive, and with that it seems _host() could create case sensitive domain return value , but I am not really sure of the best course of action here. But in general HTTP::Cookies could maintain consistency in terms of writing and reading domain name.

Inspect set_cookie(), add_cookie_header(), and _host() to trace how domain names are stored and looked up. Confirm the intended casing behavior and add regression coverage showing that cookies set for the reported domain are found when constructing the request header.