How to Call External API Service from CRM Plugins/Custom Workflows.

 public string CallRESTAPIService(string restAPIURL, string serviceCredentials)

       {

           string jsonResponse = string.Empty;

           var uri = new Uri(restAPIURL);

           var request = WebRequest.Create(uri);

           request.Method = WebRequestMethods.Http.Get;

           request.ContentType = "application/json";

           request.Headers["Authorization"] = "Basic " + Convert.ToBase64String(Encoding.Default.GetBytes(serviceCredentials));

           try

           {

               using (var response = request.GetResponse())

               {

                   using (var reader = new StreamReader(response.GetResponseStream()))

                   {

                       jsonResponse = reader.ReadToEnd();

                   }

               }

           }

           catch (System.Exception ex)

           {

               throw ex;

           }

           return jsonResponse;

       }