why is the Configuration method of Owin Startup class is invoked before and after the page load?

Question

The Configuration method of OWIN startup class is called twice in asp.net identity application. The method is called twice i.e. before and after page load on server side. I already found one question(Why is the Configuration method of the SignalR Startup class invoked twice) related to it but it doesn't clarify me regarding what is pre-initialization and post-initialization of code. Why it is needed and will it have any performance issues in my application??

Here the the code which is running twice :

 public partial class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            ConfigureAuth(app);
        }
    }

Below is the implementation of configuration method :

 public void ConfigureAuth(IAppBuilder app)
    {
        // Configure the db context, user manager and signin manager to use a single instance per request
        app.CreatePerOwinContext(RavenContext.CreateSession);
        app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);
        app.CreatePerOwinContext<ApplicationSignInManager>(ApplicationSignInManager.Create);

        // Enable the application to use a cookie to store information for the signed in user
        // and to use a cookie to temporarily store information about a user logging in with a third party login provider
        // Configure the sign in cookie
        app.UseCookieAuthentication(new CookieAuthenticationOptions
        {
            AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
            LoginPath = new PathString("/Account/Login"),
            Provider = new CookieAuthenticationProvider
            {
                // Enables the application to validate the security stamp when the user logs in.
                // This is a security feature which is used when you change a password or add an external login to your account.  
                OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
                    validateInterval: TimeSpan.FromMinutes(30),
                    regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
            }
        });            
        app.UseExternalSignInCookie(DefaultAuthenticationTypes.ExternalCookie);
}

Answer 1

I'm not convinced it is loading before and after a page but I had a similar situation where I had a virtual directory /preview that pointed to the same folder as the root.

When I hit F5 both /preview and the / applications were instantiated - resulting in two calls to Startup.Configuration.

I just deleted /preview virtual directory and then it was only called once.

It can be difficult to put a breakpoint in Startup so try something like this to see exactly how many times the startup is initialized.

public class Startup
{
    public static Guid GlobalGuid { get; private set; }

    static Startup()
    {
        GlobalGuid = Guid.NewGuid();
    }

    public void Configuration(IAppBuilder app)
    {           
       File.AppendAllLines(@"c:\temp\Startup.txt", 
                           new[] { DateTime.Now + " initialized - " + GlobalGuid });
    }
}