No 'Configuration' method was found in class 'WebApp.Startup

The following errors occurred while attempting to load the app.
- No 'Configuration' method was found in class 'WebApp.Startup, WebApp, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
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.

解决办法：

添加Startup 类

    public partial class Startup
    {
        // 有关配置身份验证的详细信息，请访问 http://go.microsoft.com/fwlink/?LinkId=301864
        public void ConfigureAuth(IAppBuilder app)
        {
            AntiForgeryConfig.UniqueClaimTypeIdentifier = ClaimTypes.Name;
            app.UseCookieAuthentication(new CookieAuthenticationOptions
            {
                AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
                LoginPath = new PathString(IdentityExtention.AuthUrl)
            });
        }
    }

添加调用

[assembly: OwinStartup(typeof(WebApp.Startup))]

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