I've played around with this a little more, and discovered some odd behavior. I decided to get rid of the SSL stuff and see what happened. It still gave me a 403 error. When I was testing this zimlet with my test server before, (when everything was working), I was using a single hostname for the external server in the allowedDomains property in the global config area of the config_template.xml file.
With or without SSL the second example gives me a 403 error. I also tried *.domainname.tld as well. This also didn't work. When using just the hostname with either external server the zimlet works properly.