handler invocation order

Hi 

Before my own AuthenticationHandler is executed I would like to execute my own DelegatingHandler (I would like to assign a session-id in my DelegatingHandler first). How can I do that? 

app.UseBasicAuthentication("Web API", ValidateUser); 

var config = new HttpConfiguration();
WebApiConfig.Register(config);          //in Register my DelegatingHandler gets registered
app.UseWebApi(config);

I already tried to set UseBasicAuthentication after UseWebApi but then the basic authentication doesn't get executed at all...