From this question I learned that Google App Engine does not currently support SSL on \"custom domains\" (at least not as of June 2010, when that question was asked).
<
Priority:
It is at the top of the Features on Deck list.
http://code.google.com/appengine/docs/roadmap.html
Simultaneous serving:
A custom domain hosted app such as http://www.mydomain.com can still be accessed on its ssl appspot subdomain such as https://yourapp.appspot.com
Issue:
http://groups.google.com/group/google-appengine/browse_thread/thread/844dc97fbfc57bab/0c8651f00072f9ea?lnk=gst&q=ssl#0c8651f00072f9ea