* Added Const for CtxKeys

* Move CtxKey Const declarations

* Fixed tests

* fix test

* Support realms with basic authentication

* Add test for default basicauth directive in which realm is not specified

* Correct typo: missing space

* Remove 'path' subdirective

* Use RequestURI when redirecting to canonical path.

Caddy may trim a request's URL path when it starts with the path that's
associated with the virtual host. This change uses the path from the request's
RequestURI when performing a redirect.

Fix issue #1327.

* Rename redirurl to redirURL.

* Redirect to the full URL.

The scheme and host from the virtual host's site configuration is used
in order to redirect to the full URL.

* Add comment and remove redundant check.

* Store the original URL path in request context.

By storing the original URL path as a value in the request context,
middlewares can access both it and the sanitized path. The default
default FileServer handler will use the original URL on redirects.

* Replace contextKey type with CtxKey.

In addition to moving the CtxKey definition to the caddy package, this
change updates the CtxKey references in the httpserver, fastcgi, and
basicauth packages.

* httpserver: Fix reference to CtxKey

* Store name of authenticated user in basicauth for use by upstream middleware such as fastcgi and cgi.

* Use request context to transfer name of authorized user from basicauth to upstream middleware. Test retrieval of name from context.

* Remove development code that was inadvertently left in place

* Use keys of type httpserver.CtxKey to access Context values

If a site owner protects a path with basicauth, no need
to use the Authorization header elsewhere upstream, especially since it
contains credentials.

If this breaks anyone, it means they're double-dipping. It's usually
good practice to clear out credentials as soon as they're not needed
anymore. (Note that we only clear credentials after they're used,
they stay for any other reason.)

* Add default "Restricted" realm to HTTP Basic auth

* Add tests for the Basic auth realm

Thanks to @jaredfolkins for the feedback