Paypal REST api call works from cURL but not from C# code

Question

I'm trying to call Paypal api from my code. I set up the sandbox account and it works when I use curl but my code isn't working the same way, returning 401 Unauthorized instead.

Here's the curl command as documented by Paypal

curl https://api.sandbox.paypal.com/v1/oauth2/token -H "Accept: application/json" -H "Accept-Language: en_US" -u "A****:E****" -d "grant_type=client_credentials" 

UPDATE: Apparently the .Credentials doesn't do the trick, instead setting Authorization header manually works (see code)

Here's the code (trimmed to its essence):

  HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("https://api.sandbox.paypal.com/v1/oauth2/token");
  request.Method = "POST";
  request.Accept = "application/json";
  request.Headers.Add("Accept-Language:en_US")

  // this doesn't work:
  **request.Credentials = new NetworkCredential("A****", "E****");**

  // DO THIS INSTEAD
  **string authInfo = Convert.ToBase64String(System.Text.Encoding.Default.GetBytes("A****:E****"));**
  **request.Headers["Authorization"] = "Basic " + authInfo;**

  using (StreamWriter swt = new StreamWriter(request.GetRequestStream()))
  {
    swt.Write("grant_type=client_credentials");
  }

  request.BeginGetResponse((r) =>
  {
    try
    {
       HttpWebResponse response = request.EndGetResponse(r) as HttpWebResponse; // Exception here
       ....
    } catch (Exception x)  { .... } // log the exception - 401 Unauthorized
  }, null);

This is the request from code captured by Fiddler (raw), there are no authorization parameters for some reason:

POST https://api.sandbox.paypal.com/v1/oauth2/token HTTP/1.1
Accept: application/json
Accept-Language: en_US
Host: api.sandbox.paypal.com
Content-Length: 29
Expect: 100-continue
Connection: Keep-Alive

grant_type=client_credentials

Answer 1

Hoping the following code help to anyone who is still looking for a good piece of cake to get connected to PayPal.

As many people, I've been investing a lot of time trying to get my PayPal token access without success, until I found the following:

public class PayPalClient
{
    public async Task RequestPayPalToken() 
    {
        // Discussion about SSL secure channel
        // http://stackoverflow.com/questions/32994464/could-not-create-ssl-tls-secure-channel-despite-setting-servercertificatevalida
        ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;
        ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls | SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;

        try
        {
            // ClientId of your Paypal app API
            string APIClientId = "**_[your_API_Client_Id]_**";

            // secret key of you Paypal app API
            string APISecret = "**_[your_API_secret]_**";

            using (var client = new System.Net.Http.HttpClient())
            {
                var byteArray = Encoding.UTF8.GetBytes(APIClientId + ":" + APISecret);
                client.DefaultRequestHeaders.Authorization = new System.Net.Http.Headers.AuthenticationHeaderValue("Basic", Convert.ToBase64String(byteArray));

                var url = new Uri("https://api.sandbox.paypal.com/v1/oauth2/token", UriKind.Absolute);

                client.DefaultRequestHeaders.IfModifiedSince = DateTime.UtcNow;

                var requestParams = new List<KeyValuePair<string, string>>
                            {
                                new KeyValuePair<string, string>("grant_type", "client_credentials")
                            };

                var content = new FormUrlEncodedContent(requestParams);
                var webresponse = await client.PostAsync(url, content);
                var jsonString = await webresponse.Content.ReadAsStringAsync();

                // response will deserialized using Jsonconver
                var payPalTokenModel = JsonConvert.DeserializeObject<PayPalTokenModel>(jsonString);
            }
        }
        catch (System.Exception ex)
        {
            //TODO: Log connection error
        }
    }
}

public class PayPalTokenModel 
{
    public string scope { get; set; }
    public string nonce { get; set; }
    public string access_token { get; set; }
    public string token_type { get; set; }
    public string app_id { get; set; }
    public int expires_in { get; set; }
}

This code works pretty well for me, hoping for you too. The credits belong to Patel Harshal who posted his solution here.