Classes in the System.Net, System.Net.Http, and System.Net.Http.Headers namespaces can be used to develop Windows Store apps or desktop apps. When used in a Windows Store app, classes in these namespaces are affected by network isolation, part of the application security model used by the Windows 8. The appropriate network capabilities must be enabled in the app manifest for a Windows Store app for the system to allow network access.
Checklist for Network Isolation
Use this checklist to be sure that network isolation is configured for your Windows Store app.
Determine the direction of network access requests needed by the app. This can be either outbound client-initiated requests or inbound unsolicited requests or it could be a combination of both of these network request types.
Determine the type of network resources that that app will communicate with. An app may need to communicate with trusted resources on a Home or Work network. An app might need to communicate with resources on the Internet. An app might need access to both types of network resources.
Configure the minimum-required networking isolation capabilities in the app manifest.
Deploy and run your app to test it using the network isolation tools provided for troubleshooting.
For more detailed information on how to configure network capabilities and isolation tools used for troubleshooting network isolation, see How to configure network isolation capabilities in the Windows 8.x Store developer documentation.
Connecting to a web service
Guidelines and checklist for network isolation
Quickstart: Connecting using HttpClient
How to use HttpClient handlers
How to secure HttpClient connections