Asp.net 4.8 WebForms authorization using Owin OpenId Connect Authentication (app.UseOpenIdConnectAuthentication)

Question

I am encountering an infinite redirect loop between login.microsoftonline.com and my application. My project is implementing authentication and authorization in an Asp.net 4.8 web forms project. I am able to add authentication using the default Owin startup file and then require authentication in the web config file. The below works correctly for requiring a user to sign in before being able to access pages/AuthRequired

StartupAuth.CS

public partial class Startup
    {
        private static string clientId = ConfigurationManager.AppSettings["ida:ClientId"];
        private static string postLogoutRedirectUri = ConfigurationManager.AppSettings["ida:PostLogoutRedirectUri"];
        private static string authority = ConfigurationManager.AppSettings["ida:Authority"];
        private static string clientSecret = ConfigurationManager.AppSettings["AppRegistrationSecret-Local"];
        public void ConfigureAuth(IAppBuilder app)
        {
            //for debugging
            //IdentityModelEventSource.ShowPII = true;

            app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

            app.UseCookieAuthentication(new CookieAuthenticationOptions());
            app.UseOpenIdConnectAuthentication(
                new OpenIdConnectAuthenticationOptions
                {
                    ClientId = clientId,
                    Authority = authority,
                    PostLogoutRedirectUri = postLogoutRedirectUri,
                    ClientSecret = clientSecret,
                    RedirectUri = postLogoutRedirectUri,
                    //This allows multitenant
                    //https://github.com/Azure-Samples/guidance-identity-management-for-multitenant-apps/blob/master/docs/03-authentication.md
                    TokenValidationParameters = new TokenValidationParameters
                    {
                        ValidateIssuer = false
                    },

                    Notifications = new OpenIdConnectAuthenticationNotifications()
                    {
                        AuthenticationFailed = (context) =>
                        {
                            return Task.FromResult(0);
                        }
                    }
                }
                );

            // This makes any middleware defined above this line run before the Authorization rule is applied in web.config
            app.UseStageMarker(PipelineStage.Authenticate);
        }
    }

Web.Config

<configuration>
...
    <system.web>
        <authentication mode="None" />
    </system.web>
    <location path="Pages/AuthRequired">
        <system.web>
            <authorization>
                <deny users="?" />
            </authorization>
        </system.web>
    </location>
    <system.webServer>
        <modules>
            <remove name="FormsAuthentication" />
        </modules>
    </system.webServer>
...
</configuration>

I need to add authorization so that only users with the admin role will be able to access Pages/AuthRequired. I have done that by updating the web config:

<configuration>
...
    <system.web>
        <authentication mode="None" />
    </system.web>
    <location path="Pages/AuthRequired">
        <system.web>
            <authorization>
                <allow roles="Admin" />
                <deny users="*" />
            </authorization>
        </system.web>
    </location>
    <system.webServer>
        <modules>
            <remove name="FormsAuthentication" />
        </modules>
    </system.webServer>
...
</configuration>

Adding authorization to the authenticated page works correctly if the user has that role, but if a user who doesn't have the role tries to access the page they are redirected back to login.microsoftonline.com and then back to the application in an infinite loop.

I can see that Owin UseOpenIdConnectAuthentication is returning a 302 response on unauthorized and that is causing the loop.

How can I change it so that instead of redirecting unauthorized (but authenticated) users to login.microsoftonline.com, that user should be directed to an app page that displays a 401 error?

Answer 1

Please check if below work around helps:

Its usually possible that if forms authentication is enabled, you will be redirected to the login page when status code is 401.

As a workaround try Adding the below to global.asax in the application end request and you can create own unauthorized page if needed and redirect to that.

if (this.Response.StatusCode == 302&& this.Response.StatusCode == 401 
        && this.Response.RedirectLocation.ToLower().Contains("login.aspx"))
      {
        this.Response.StatusCode = 401;
         //or Response.Redirect("Unauthorized.aspx");
      }
      

You can also check this > Redirect unauthorised user to message page in ASP .Net. (microsoft.com)

Other references

1. Prevent redirect to login on status code 401 (Unauthorized) (microsoft.com)
2. asp.net - In-place handling (no redirect) of 401 unauthorized? - Stack Overflow