fix(lib): properly clear out test cookie (#522)

Closes #520

For some reason, Chrome and Firefox are very picky over what they use to
match cookies that need to be deleted. Listen to me for my tale of woe:

The basic problem here is that cookies were an early hack added on the
side of the HTTP spec and they're basically impossible to upgrade or
change because who knows what relies on the exact behavior cookies use.
As a result, cookies don't just match by name, but by every setting that
exists on them. You can also have two cookies with the same name but
different values. This spec is a nightmare lol.

Even more fun: browsers will make up values for cookies if they aren't
set, meaning that getting a challenge token at `/docs` is semantically
different than a challenge token you got from `/`.

This PR fixes this issue by explicitly setting the "make sure cookie
support is working" cookie's path to `/`, meaning that it will always be
sent. Additionally, cookies are expired by setting the expiry time to
one minute in the past.

Hopefully this will fix it. I'm testing this locally and it seems to
work fine.

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/http_test.go

@@ -11,7 +11,7 @@ func TestClearCookie(t *testing.T) {
 	srv := spawnAnubis(t, Options{})
 	rw := httptest.NewRecorder()
 
-	srv.ClearCookie(rw, srv.cookieName)
+	srv.ClearCookie(rw, srv.cookieName, "/")
 
 	resp := rw.Result()
 
@@ -36,7 +36,7 @@ func TestClearCookieWithDomain(t *testing.T) {
 	srv := spawnAnubis(t, Options{CookieDomain: "techaro.lol"})
 	rw := httptest.NewRecorder()
 
-	srv.ClearCookie(rw, srv.cookieName)
+	srv.ClearCookie(rw, srv.cookieName, "/")
 
 	resp := rw.Result()