rewrite if user is NOT authenticated

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My IIS site ("https://mysite.com") is protected by SSL and basic authentication. Requests are reverse-proxied to the internal server "haus.lan" with the following rule:

Code: Select all

RewriteRule (.*)$ http://haus.lan/$1 [nocase, P, last]

In addition to the above, I now need to allow SSL requests from unauthenticated users requesting Amazon Alexa services, and reverse-proxy them to a different internal server ("alexa.lan"). This requests has to obligatorily go through port 443 and SSL, but it must not require userid/password (per Amazon's regulations for Alexa skill developers).

Can I accomplish the above? basically, Isapi_rewrite should intercept the pattern "https://mysite.com/alexa" and reverse proxy it to the internal site "http://alexa.lan" without requesting basic auth. Any help would be greatly appreciated!