How to set the HTTP headers "X-Forwarded-Context" or "X-Forwarded-Prefix" with IIS reverse proxy

Question

I try to configure a reverse proxy in the IIS. This required to set some HTTP headers. I was able to add the follow HTTP headers:

• X-Forwarded-Proto
• X-Forwarded-Port
• X-Forwarded-Host

This is possible by adding and setting server variables with related names. The webconfig look like:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
        <rewrite>
            <rules>
                <rule name="ReverseProxyInboundRule1" stopProcessing="true">
                    <match url="^foobar(.*)" />
                    <action type="Rewrite" url="http://localhost:9999/{R:1}" />
                    <serverVariables>
                        <set name="HTTP_X_FORWARDED_PORT" value="80" />
                        <set name="HTTP_X_FORWARDED_HOST" value="localhost" />
                        <set name="HTTP_X_FORWARDED_PROTO" value="http" />
                        <set name="HTTP_X_FORWARDED_PREFIX" value="/foobar" />
                        <set name="HTTP_X_FORWARDED_CONTEXT" value="/foobar" />
                    </serverVariables>
                </rule>
            </rules>
        </rewrite>
    </system.webServer>
</configuration>

But I'm out of luck for the HTTP headers X-Forwarded-Context or X-Forwarded-Prefix. Also adding the server variables has no effect.