No assembly found containing an OwinStartupAttribute.

No assembly found containing an OwinStartupAttribute.

While I'm trying to deploy the IdentityServer3 by looking at its Github documentation and manual, I encountered this error at the first trial to run the server. It's been a while since I tweak some codes on a web project, I was a bit frustrated by this error. Things to notice from the error logs below...

[EntryPointNotFoundException: The following errors occurred while attempting to load the app.
- No assembly found containing an OwinStartupAttribute.
- No assembly found containing a Startup or [AssemblyName].Startup class.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.]
Microsoft.Owin.Host.SystemWeb.OwinBuilder.GetAppStartup() +357
Microsoft.Owin.Host.SystemWeb.OwinHttpModule.InitializeBlueprint() +28
System.Threading.LazyInitializer.EnsureInitializedCore(T& target, Boolean& initialized, Object& syncLock, Func`1 valueFactory) +115
Microsoft.Owin.Host.SystemWeb.OwinHttpModule.Init(HttpApplication context) +106
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +536
System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +173
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +336
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +296

[HttpException (0x80004005): The following errors occurred while attempting to load the app.
- No assembly found containing an OwinStartupAttribute.
- No assembly found containing a Startup or [AssemblyName].Startup class.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +10085804
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +95
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +254




are these two lines.




		 - No assembly found containing an OwinStartupAttribute.
 - No assembly found containing a Startup or [AssemblyName].Startup class.
	




It literally says that there's no assembly found on the Startup class, that is related to Owin. Unfortunately there's no further information about this error in the github GettingStarted section. It just shows us this block of codes below.




public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.Map("/identity", idsrvApp =>
            {
                idsrvApp.UseIdentityServer(new IdentityServerOptions
                {
                    SiteName = "Embedded IdentityServer",
                    SigningCertificate = LoadCertificate(),

                    Factory = new IdentityServerServiceFactory()
                                .UseInMemoryUsers(Users.Get())
                                .UseInMemoryClients(Clients.Get())
                                .UseInMemoryScopes(StandardScopes.All)
                });
            });
    }

    X509Certificate2 LoadCertificate()
    {
        return new X509Certificate2(
            string.Format(@"{0}\bin\identityServer\idsrv3test.pfx", AppDomain.CurrentDomain.BaseDirectory), "idsrv3test");
    }
}




From : https://identityserver.github.io/Documentation/docsv2/overview/mvcGettingStarted.html







So if you just stick to this code, you're doomed to see the error for sure. No help is provided in the GettingStarted section for that error. Maybe it's so easy and so basic that they would have decided to skip some help tips, thinking developers would get through with it.

Anyway, this is the solution for this.




Solution

[assembly: OwinStartup(typeof(YourNamespace.Startup))]
namespace YourProjectNamespace 
.
.
.
public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.Map("/identity", idsrvApp =>
            {
                idsrvApp.UseIdentityServer(new IdentityServerOptions
                {
                    SiteName = "Embedded IdentityServer",
                    SigningCertificate = LoadCertificate(),

                    Factory = new IdentityServerServiceFactory()
                                .UseInMemoryUsers(Users.Get())
                                .UseInMemoryClients(Clients.Get())
                                .UseInMemoryScopes(StandardScopes.All)
                });
            });
    }

    X509Certificate2 LoadCertificate()
    {
        return new X509Certificate2(
            string.Format(@"{0}\bin\identityServer\idsrv3test.pfx", AppDomain.CurrentDomain.BaseDirectory), "idsrv3test");
    }
}		

Just attach the assembly annotation above the namespace of the startup class.

FYI, it's Microsoft.Owin assembly that let you use OwinStartup constructor in there.

You will see a proper web page after build your project.