What does HostAuthenticationFilter do?

Question

Can somone please explain what these two lines of code mean inside the Register() method of my WebApiConfig.cs file.

// Web API configuration and services
// Configure Web API to use only bearer token authentication.
config.SuppressDefaultHostAuthentication();
config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

I assume its adding HostAuthentication application wide. But even if I don't pass a bearer token with my requests I am still able to get the data. So whats the point of adding this filter?

Answer 1

I usually keep the following comments in my code as a reminder of what they are for.

// Configure Web API to use only bearer token authentication.
// If you don't want the OWIN authentication to flow to your Web API then call 
// SuppressDefaultHostAuthentication on your HttpConfiguration. 
// This blocks all host level authentication at that point in the pipeline.
config.SuppressDefaultHostAuthentication();
//config.Filters.Add(new HostAuthenticationFilter(Microsoft.Owin.Security.OAuth.OAuthDefaults.AuthenticationType));

// “Host-level authentication” is authentication performed by the host (such as IIS), 
// before the request reaches the Web API framework. 
// ----
// Often, you may want to to enable host-level authentication for the rest of your application, 
// but disable it for your Web API controllers. For example, a typical scenario is to 
// enable Forms Authentication at the host level, but use token-based authentication for Web API.
// ----
// To disable host-level authentication inside the Web API pipeline, call config.SuppressHostPrincipal() 
// in your configuration. This causes Web API to remove the IPrincipal from any request that enters 
// the Web API pipeline. Effectively, it "un-authenticates" the request.
config.SuppressHostPrincipal();

Also if you are still getting access to action data, chances are you did not apply [Authorize] attribute to the controller or action to restrict access.

Related reading Host authentication and Web API with OWIN and active vs. passive authentication middleware