Oauth2 Yahoo Gemini API - oauth-2.0

Question

I am having trouble calling Yahoo Gemini API to access Yahoo Gemini Advertising from my C# console (desktop) application.
Here are steps I used:
Create an installed application on https://developer.yahoo.com/apps/create/. This gave me both {Client ID} and {Client Secret}.
https://api.login.yahoo.com/oauth2/request_auth?client_id={Client ID} &redirect_uri=oob&response_type=code&language=en-us. This will take me to the yahoo login screen where I sign in. Press the Agree button and the next screen shows the seven-letter authorization code (say nzbcns9). I write down this authorization code.
Then I use the following code to try to get the access token:
class Program
{
static void Main(string[] args)
{
string clientId = {Client ID};
string secret = {Client Secret};
var request = WebRequest.Create(#"https://api.login.yahoo.com/oauth2/get_token");
request.Method = "POST";
SetBasicAuthHeader(request, clientId, secret);
string postData = "grant_type=authorization_code&redirect_uri=oob&code=nzbcns9";
ASCIIEncoding encoding = new ASCIIEncoding();
byte[] byte1 = encoding.GetBytes(postData);
request.ContentLength = byte1.Length;
Stream dataStream = request.GetRequestStream();
dataStream.Write(byte1, 0, byte1.Length);
dataStream.Close();
request.ContentType = "application/x-www-form-urlencoded";
var response = request.GetResponse();
Console.WriteLine(((HttpWebResponse)response).StatusDescription);
}
static void SetBasicAuthHeader(WebRequest request, String userName, String userPassword)
{
string authInfo = userName + ":" + userPassword;
authInfo = Convert.ToBase64String(Encoding.Default.GetBytes(authInfo));
request.Headers["Authorization"] = "Basic " + authInfo;
}
}
Then I get
Unhandled Exception: System.Net.WebException: The remote server returned an error: (401) Unauthorized. at System.Net.HttpWebRequest.GetResponse().
What did I do wrong?
I also try to post the same message using Fiddler, I get
{"error":"invalid_request"}

Answer 1

I tried your code and what worked for me was to put the line request.ContentType = "application/x-www-form-urlencoded"; BEFORE Stream dataStream = request.GetRequestStream();
So this worked:
string postData = "grant_type=authorization_code&redirect_uri=oob&code=nzbcns9";
ASCIIEncoding encoding = new ASCIIEncoding();
byte[] byte1 = encoding.GetBytes(postData);
request.ContentLength = byte1.Length;
request.ContentType = "application/x-www-form-urlencoded";
Stream dataStream = request.GetRequestStream();
dataStream.Write(byte1, 0, byte1.Length);
dataStream.Close();

Answer 2

Neither of these worked for me, but it did work once I changed the SetBasicAuthHeader to use ISO-8859-1 encoding:
static void SetBasicAuthHeader( WebRequest request, String userName, String userPassword )
{
string authInfo = userName + ":" + userPassword;
authInfo = Convert.ToBase64String( Encoding.GetEncoding( "ISO-8859-1" ).GetBytes( authInfo ) );
request.Headers[ "Authorization" ] = "Basic " + authInfo;
}