Consume WebService Using HTTP Request

Your question is not clear, but here is some code which could help you starting...

If this is your rest service:

[DataContract]
[Serializable]
public class SendData
{
    [DataMember(Order=1)]
    public string cmd;

    [DataMember(Order=2)]
    public string data;
}

namespace My_Server
{
    [ServiceContract]
    public interface IRestService
    {
        [WebInvoke(Method = "POST", 
		UriTemplate = "logon", 
		RequestFormat = WebMessageFormat.Xml, 
		ResponseFormat = WebMessageFormat.Xml, 
		BodyStyle = WebMessageBodyStyle.Bare)]
        [OperationContract]
        LogonResult DoLogon(SendData data);
    }
}

...then your client cmd could look like this:

private void DoLogon(string credentials)
{
    SendData sd = new SendData();
    sd.cmd = "EXTERNAL-USER";
    sd.data = credentials;
    XmlDocument xdoc = HttpPost("https://yourserver-ip:443/internal/logon", sd);
    // convert xml document from the server to object of type LogonResult
    DataContractSerializer dcSer = new DataContractSerializer(typeof(LogonResult));
    StringWriter stringWriter = new StringWriter();
    XmlTextWriter xmlWriter = new XmlTextWriter(stringWriter);
    xdoc.WriteTo(xmlWriter);
    MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(stringWriter.ToString()));
    stream.Position = 0;
    XmlDictionaryReader reader = XmlDictionaryReader.CreateTextReader(stream, new XmlDictionaryReaderQuotas());
    LogonResult res = (LogonResult)dcSer.ReadObject(reader, true);
            
do something with the result...    
}

The class library to share between server and client:

namespace DataLib
{
    [Serializable]
    public class LogonResult
    {
        public bool bCmdSuccess;
        public string sInfo;
    }
}