Update README.md

Add additional boolean 'useAppPoolIdentity' property to the ServerUrl object that will trump the 'domain', 'username' and 'password' properties.  This 'useAppPoolIdentity' will inherit the configured IIS Application Pool identity by using the 'CredentialCache.DefaultNetworkCredentials' in 'System.Net' .

README.md

@@ -57,7 +57,7 @@ All three proxies respect the XML configuration properties listed below.
     * **username**: Username to use when requesting a token - if needed for ArcGIS Server token based authentication.
     * **password**: Password to use when requesting a token - if needed for ArcGIS Server token based authentication.
     * **tokenServiceUri**: If username and password are specified, the proxy will use the supplied token service uri to request a token.  If this value is left blank, the proxy will request a token URL from the ArcGIS server.
-    * **domain**: The Windows domain to use with username/password when using Windows Authentication. Only applies to DotNet proxy.
+* **useAppPoolIdentity**: The IIS application pool identity will be used for authenticating with secured resources.  This configuration will supersede the domain, username, and password configurations.  Only applies to DotNet proxy.    * **domain**: The Windows domain to use with username/password when using Windows Authentication. Only applies to DotNet proxy.
     * **clientId**.  Used with clientSecret for OAuth authentication to obtain a token - if needed for OAuth 2.0 authentication. **NOTE**: If used to access hosted services, the service(s) must be owned by the user accessing it, (with the exception of credit-based esri services, e.g. routing, geoenrichment, etc.)
     * **clientSecret**: Used with clientId for OAuth authentication to obtain a token - if needed for OAuth 2.0 authentication.
     * **oauth2Endpoint**: When using OAuth 2.0 authentication specify the portal specific OAuth 2.0 authentication endpoint. The default value is https://www.arcgis.com/sharing/oauth2/.