Ignore trailing . in hostnames.

This means that e.g. `https://site.tld.` will be treated the same as
`https://site.tld`. In DNS, the trailing empty label means "root domain"
and is usually ignored when present. There are some sites with links
that don't work otherwise.

src/auth.go

@@ -52,6 +52,7 @@ func GetHost(r *http.Request) (string, error) {
 		return "", AuthError{http.StatusBadRequest,
 			fmt.Sprintf("host name %q is reserved", host)}
 	}
+	host = strings.TrimSuffix(host, ".")
 	return host, nil
 }