C# authorization in HTTP request Plivo API

Question

I am trying to use Plivo to send text messages from within my WindowsStore Application. Here is what almost works:

// These first 3 lines don't do what I want
var unamepass = AuthID + ":" + AuthToken;
var auth = new HttpCredentialsHeaderValue("Basic", unamepass);
httpClient.DefaultRequestHeaders.Authorization = auth;

string textBody = "sample message";
var plivoText = new
{
    src = plivoNumber,
    dst = phoneNumber,
    text = textBody
};
string Serial = JsonConvert.SerializeObject(plivoText);
IHttpContent PlivoJsonContent = new HttpJsonContent(JsonValue.Parse(Serial));
HttpResponseMessage PlivoResponse = 
    await httpClient.PostAsync(
        new Uri("https://api.plivo.com/v1/Account/<AuthID>/Message/")
        , PlivoJsonContent);

Now, this code works... technically. I get a 202 response back. However, before it sends the text, a large authentication pops onto the screen.

If I enter the correct data I get a 202 and the text sends, otherwise I can't send the data. I want to know how to programmatically add this to the request, so I don't have to do it manually. I'm pretty sure it has something to do with the first 3 lines of the snippet, but the documentation I found online wasn't very helpful to me. I can't use RestSharp because it isn't supported for windows store projects, so I would prefer an HttpClient solution.

What "scheme" does Plivo use? How should I construct HttpCredentialsHeaderValue? Is the 3rd line correct?

Answer 1

The answer was startlingly simple. You must convert the string to base64 in order to send it to the header.

See: Convert UTF-8 to base64 string