Complete Reverse proxy rule for SharePoint

web.config

<configuration>
  <system.serviceModel>
      <serviceHostingEnvironment aspNetCompatibilityEnabled="true" multipleSiteBindingsEnabled="true" />
  </system.serviceModel>
  
  <system.webServer>
    <modules runAllManagedModulesForAllRequests="true">
          <add name="CustomHttpModule" type="Custom.ServerModules.CustomHttpHeaderModule" />
    </modules>
    <httpProtocol>
          <customHeaders>
              <clear />
              <remove name="X-Powered-By" />
              <add name="X-Frame-Options" value="SAMEORIGIN" /> 
          </customHeaders>
      </httpProtocol>
     <rewrite>          
          <rules>             
             <rule name="ReverseProxy" stopProcessing="true">
                  <match url=".*" />
                  <conditions logicalGrouping="MatchAll" trackAllCaptures="false">
                      <add input="{HTTP_HOST}" pattern="portal.contoso.com" />
                  </conditions>
                  <action type="Rewrite" url="http://internalserver:2000/{R:0}" />
                  <serverVariables>
                      <set name="HTTP_X_ACCEPT_ENCODING" value="{HTTP_ACCEPT_ENCODING}" /> 
                      <set name="HTTP_X_ORIGINAL_HOST" value="{HTTP_HOST}" />
                      <set name="HTTP_ACCEPT_ENCODING" value=""/>
                  </serverVariables>
              </rule>
          </rules>
     </rewrite>
  </system.webServer>
  </configuration>