Two simple steps to enable HTTPS for ASP.NET Web API service. 

Step 1 : Right click on the ASP.NET Web API project and add a class file. Name it RequireHttpsAttribute. Copy and paste the following code

using System; using System.Net; using System.Net.Http; using System.Text; using System.Web.Http.Controllers; using System.Web.Http.Filters;   namespace EmployeeService {     public class RequireHttpsAttribute : AuthorizationFilterAttribute     {         public override void OnAuthorization(HttpActionContext actionContext)         {             if (actionContext.Request.RequestUri.Scheme != Uri.UriSchemeHttps)             {                 actionContext.Response = actionContext.Request                     .CreateResponse(HttpStatusCode.Found);                 actionContext.Response.Content = new StringContent                     ("<p>Use https instead of http</p>", Encoding.UTF8, "text/html");                   UriBuilder uriBuilder = new UriBuilder(actionContext.Request.RequestUri);                 uriBuilder.Scheme = Uri.UriSchemeHttps;                 uriBuilder.Port = 44337;                   actionContext.Response.Headers.Location = uriBuilder.Uri;             }             else             {                 base.OnAuthorization(actionContext);             }         }     } }

Step 2 : Include the following line of code in Register() method of WebApiConfig class in WebApiConfig.cs file in App_Start folder. This adds RequireHttpsAttribute as a filter to the filters collection. So for every request the code in this filter is executed. If the request is issued using HTTP, it will be automatically redirected to HTTPS.

config.Filters.Add(new RequireHttpsAttribute());

Please note : If you don't want to enable HTTPS for the entire application then don't add RequireHttpsAttribute to the filters collection on the config object in the register method. Simply decorate the controller class or the action method with RequireHttpsAttribute for which you want HTTPS to be enabled. For the rest of the controllers and action methods HTTPS will not be enabled.