I used this code over https to do basic authentication from wp7 to mvc 4 beta with web api

BasicAuthWp7.cs

// I used this article to get the headers right. 
// http://cisforcoder.wordpress.com/2010/12/01/how-to-implement-basic-http-authentication-in-wcf-on-windows-phone-7/ 
// The commented out NetworkCredential that I had tried earlier didn't work.
// I wonder if there is a better way to do this in Mango? 
//
// Would like to learn to use asp.net membership with web api from the phone and metro.
// this works for now. 

       private void btnTest_Click(object sender, System.Windows.RoutedEventArgs e)
        {
            WebClient client = new WebClient();
            client.DownloadStringCompleted += new 
                DownloadStringCompletedEventHandler(client_DownloadStringCompleted);

            //NetworkCredential credentials = 
            //    new NetworkCredential(settings.Login, settings.Password);
            //client.Credentials = credentials;

            var credentials = EncodeBasicAuthenticationCredentials(settings.Login, settings.Password);
            client.Headers[System.Net.HttpRequestHeader.Authorization] = "Basic " + credentials;
            client.DownloadStringAsync(new Uri(@"https://www.TheSiteIHaveItOn.com/api/Sounds"));
        }

        private string EncodeBasicAuthenticationCredentials(string username, string password)
        {
            //first concatenate the user name and password, separated with :
            string credentials = username + ":" + password;

            //Http uses ascii character encoding, WP7 doesn’t include
            // support for ascii encoding but it is easy enough to convert
            // since the first 128 characters of unicode are equivalent to ascii.
            // Any characters over 128 can’t be expressed in ascii so are replaced
            // by ?
            var asciiCredentials = (from c in credentials
                                    select c <= 0x7f ? (byte)c : (byte)'?').ToArray();

            //finally Base64 encode the result
            return Convert.ToBase64String(asciiCredentials);
        }

        void client_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
        {
            Debug.WriteLine(e.ToString()); 
        }