Consuming REST Service pb - asp.net

Question

I'm having some problem consuming REST Service and want to figure out what I'm missing in implementation.
https://<server-name-or-address>/api/sessions
if I call this rest api using cURL, it works just fine by following script
curl -i -k -H "Accept:application/*+xml;version=1.5" -u username:password -X POST https://<server-name-or-address>/api/sessions
However, it isn't working at all with C# asp.net. I'm not sure what I'm missing here. Here are my attempts:
1) Using HTTP Web Request
Uri address = new Uri(url);
HttpWebRequest request = WebRequest.Create(address) as HttpWebRequest;
request.Method = "POST";
request.Accept = "application/*+xml;version=1.5";
request.Credentials = new NetworkCredential(username,password);
HttpWebResponse response = request.GetResponse() as HttpWebResponse;
// following exception fires on calling aforementioned statement
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel.
2) Using Hammock.net
Hammock.RestClient client = new Hammock.RestClient();
string encodedAPIKey = Convert.ToBase64String(Encoding.UTF8.GetBytes(string.Format("{0}:{1}", username, password)));
client.AddHeader("Accept", "application/*+xml;version=1.5");
client.AddHeader("Authorization", "Basic " + username + ":" + password);
client.Authority = url;
Hammock.RestRequest req = new Hammock.RestRequest();
req.Path = url;
Hammock.RestResponse response = client.Request(req);
string _result = client.Request(req).Content; // exception
3) Using RestSharp
string _loginInfo = Convert.ToBase64String(Encoding.UTF8.GetBytes(string.Format("{0}:{1}", username, password)));
RestSharp.RestClient client = new RestSharp.RestClient();
client.AddDefaultHeader("Accept", "application/*+xml;version=1.5");
client.AddDefaultHeader("Authorization", "Basic " + _loginInfo);
client.BaseUrl = url;
RestSharp.RestRequest request = new RestSharp.RestRequest();
request.AddUrlSegment("method", "POST");
request.AddUrlSegment("uri", url);
string result = client.Execute(request).Content;
I also have tried with HttpClient, WebRequest, WebClient though nothing appears to work.

Answer 1

Try manually setting the Authorization header yourself in the HTTP request.
string credentials = String.Format("{0}:{1}", username, password);
byte[] bytes = Encoding.ASCII.GetBytes(credentials);
string base64 = Convert.ToBase64String(bytes);
string authorization = String.Concat("Basic ", base64);
request.Headers.Add("Authorization", authorization);
EDIT:
It looks as though it may be due to a self-signed, expired, or otherwise invalid cert. Try the following
ServicePointManager.ServerCertificateValidationCallback = delegate { return true; };
Gleaned from this SO: https://stackoverflow.com/questions/5595049/servicepointmanager-servercertificatevalidationcallback-question