Azure App Service Reverse Proxy works only on port 80 http - iis

Question

I'm trying to configure Azure App Service Reverse Proxy to expose webserver in Azure Virtual Network to the internet and I had limited success - it's working when I'm not using encrypted connection between reverse proxy and target server.
Here is my currently working configuration:
web.config
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.webServer>
<httpErrors errorMode="Detailed" />
<rewrite>
<rules>
<rule name="ForceSSL" stopProcessing="true">
<match url="(.*)" />
<conditions>
<add input="{HTTPS}" pattern="^OFF$" ignoreCase="true" />
</conditions>
<action type="Redirect" url="https://{HTTP_HOST}/{R:1}" redirectType="Permanent" />
</rule>
<rule name="Proxy" stopProcessing="true">
<match url="(.*)" />
<action type="Rewrite" url="http://example.com/{R:1}" />
<serverVariables>
<set name="HTTP_X_UNPROXIED_URL" value="http://example.com/{R:1}" />
<set name="HTTP_X_ORIGINAL_ACCEPT_ENCODING" value="{HTTP_ACCEPT_ENCODING}" />
<set name="HTTP_X_ORIGINAL_HOST" value="{HTTP_HOST}" />
<set name="HTTP_ACCEPT_ENCODING" value="" />
</serverVariables>
</rule>
</rules>
<outboundRules>
<preConditions>
<preCondition name="CheckContentType">
<add input="{RESPONSE_CONTENT_TYPE}" pattern="^(text/html|text/plain|text/xml|application/rss\+xml)" />
</preCondition>
</preConditions>
</outboundRules>
</rewrite>
</system.webServer>
</configuration>
applicationHost.xdt
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<system.webServer>
<proxy xdt:Transform="InsertIfMissing" enabled="true" preserveHostHeader="false" reverseRewriteHostInResponseHeaders="false"/>
<rewrite xdt:Transform="InsertIfMissing">
<allowedServerVariables xdt:Transform="InsertIfMissing">
<add name="HTTP_X_ORIGINAL_HOST" xdt:Transform="InsertIfMissing" xdt:Locator="Match(name)"/>
<add name="HTTP_X_UNPROXIED_URL" xdt:Transform="InsertIfMissing" xdt:Locator="Match(name)"/>
<add name="HTTP_X_ORIGINAL_ACCEPT_ENCODING" xdt:Transform="InsertIfMissing" xdt:Locator="Match(name)"/>
<add name="HTTP_ACCEPT_ENCODING" xdt:Transform="InsertIfMissing" xdt:Locator="Match(name)"/>
</allowedServerVariables>
</rewrite>
</system.webServer>
</configuration>
IP Address of the server has been replaced by example.com
When I change web.config rewrite rule and HTTP_X_UNPROXIED_URL to https I get following IIS Error
Detailed Error Information:
Module ApplicationRequestRouting
Notification ExecuteRequestHandler
Handler ApplicationRequestRoutingHandler
Error Code 0x80072f8f
Requested URL https://example.com:80/
Physical Path D:\home\site\wwwroot
Logon Method Anonymous
Logon User Anonymous
Request Tracing Directory D:\home\LogFiles
This suggests, that for some reason it's trying to request https on port 80.
I tried to follow guide from here: https://www.patrickob.com/2018/11/10/adding-ca-certs-to-the-trusted-root-store-for-web-apps-hosted-in-an-ase/
I have added my organizations root cert to SSL certificated and added WEBSITE_LOAD_ROOT_CERTIFICATES setting.
Any help will be appreciated.

Answer 1

WEBSITE_LOAD_ROOT_CERTIFICATES is only supported in an App Service Environment, its not supported in multi-tenant app services. If the endpoint on-premises is signed by a certificate not using a public CA at this time there's no direct workaround to make this work outside of updating the certificate or possibly writing a simple proxy app that can ignore SSL cert validation (I typically wouldn't recommend this option unless you do the cert validation yourself in code).