[warn] proxy: No protocol handler was valid for the url /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
Does this sound like you?
ProxyPass /foo/ https://example.com/bar/
ProxyPassReverse /foo/ https://example.com/bar/
Solution: Purge the apache-ssl package. Go into the Debian Stable NonUS category -- if you don't have it, run apt-setup, or manually add nonus.debian.org to your /etc/apt/sources.list , and find the libapache-mod-ssl package. Installing it will bring plain "apache" with it as a dependency.
Spend a few minutes looking at how mod_ssl is different than apache-ssl . Set up your httpd.conf again.
Ding. It works.
I'm glad I'm not the only one who had this problem. However several people quite convincingly told me "It doesn't word, mod_proxy can't fetch https:// data.". So, I dredged around the Apache Project's CVS tree... and for Apache 1.3, they're right, mod_proxy by itself can't handle https:// (though apparently mod_ssl provides the missing hooks). Apache 2.0's source tree has mod_proxy stuff in it that looks https:// savvy though.