Using the [Authorize] attribute

AuthorizeAttribute will make sure if the user is authenticated or unauthenticated. Unauthorized error with HTTP status code 401 will be returned if the user is not authenticated and the corresponding action will not be invoked. Web API enables you to apply the filter in three ways. We can apply them at global level, or at the controller level, or at the individual action level.

Global authorization filter

To apply authorization filter for all Web API controllers, we need to add the AuthorizeAttribute filter to the global filter list in the Global.asax file as given below:

public static void Register(HttpConfiguration config)
{
    config.Filters.Add(new AuthorizeAttribute());
}

Controller level authorization filter

To apply an authorization filter for a specific controller, we need to decorate the controller with filter attribute as given in the following code:

// Require authorization for all actions on the controller.
[Authorize]
public class ContactsController : ApiController
{
    public IEnumerable<Contact> GetAllContacts() { ... }
    public IHttpActionResult GetContact(int id) { ... }
}

Action level authorization filter

To apply an authorization filter for specific actions, we need to add the attribute to the action method as given in the following code:

public class ContactsController : ApiController
{
    public IEnumerable<Contact> GetAllContacts() { ... }

    // Require authorization for a specific action.
    [Authorize]
    public IHttpActionResult GetContact(int id) { ... }
}