Testing web apps locally
When you are developing a web app, it is convenient to test the app on a local computer before you deploy it to a web server. However, the Live Connect APIs require the redirect URL to use the same domain at which the apps client ID was configured. Your local computers web server probably uses a default address like http://localhost, so you must map your domain to the Internet Protocol IP address of your local web server. To do this, you add a mapping to the hosts file on your computer. The job of the hosts file is to map host names to IP addresses. On Windows computers, the hosts file is located at \Windows\System32\drivers\etc\hosts.