Just as suggested in comments, a quick google search could lead to interesting results.
Nevertheless a possible solution is the implementation proposed in the following Microsoft article :
public class RequireHttpsAttribute : AuthorizationFilterAttribute
{
public override void OnAuthorization(HttpActionContext actionContext)
{
if (actionContext.Request.RequestUri.Scheme != Uri.UriSchemeHttps)
{
actionContext.Response = new HttpResponseMessage(System.Net.HttpStatusCode.Forbidden)
{
ReasonPhrase = "HTTPS Required"
};
}
else
{
base.OnAuthorization(actionContext);
}
}
}
You would then decorate your ApiController action :
public class SomeController : ApiController
{
[RequireHttps]
public HttpResponseMessage Get() { ... }
}