Apply [Authorize] attribute implicitly to all Web API controllers

You have two options

1. Controller level by decorating your controller with authorize attribute.

   [Authorize]
   [RoutePrefix("api/account")]
   public class AccountController : ApiController
   {
   

2. You can also set it global level to all routes, in Register method of WebApiConfig.cs file

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