Microsoft Owin Don't want to use implicit flow

Question

I am trying to get Owin working in an asp.net web app with Azure AD. Here is my startup code that configures Owin.

    public class Startup
{
    // The Client ID is used by the application to uniquely identify itself to Microsoft identity platform.
    string clientId = System.Configuration.ConfigurationManager.AppSettings["ClientId"];

    // RedirectUri is the URL where the user will be redirected to after they sign in.
    string redirectUri = System.Configuration.ConfigurationManager.AppSettings["RedirectUri"];

    // Tenant is the tenant ID (e.g. contoso.onmicrosoft.com, or 'common' for multi-tenant)
    static string tenant = System.Configuration.ConfigurationManager.AppSettings["Tenant"];

    // Authority is the URL for authority, composed by Microsoft identity platform endpoint and the tenant name (e.g. https://login.microsoftonline.com/contoso.onmicrosoft.com/v2.0)
    string authority = String.Format(System.Globalization.CultureInfo.InvariantCulture, System.Configuration.ConfigurationManager.AppSettings["Authority"], tenant);

    /// <summary>
    /// Configure OWIN to use OpenIdConnect
    /// </summary>
    /// <param name="app"></param>
    public void Configuration(IAppBuilder app)
    {
        app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);

        app.UseCookieAuthentication(new CookieAuthenticationOptions());
        app.UseOpenIdConnectAuthentication(
            new OpenIdConnectAuthenticationOptions
            {
            // Sets the ClientId, authority, RedirectUri as obtained from web.config
            ClientId = clientId,
                Authority = authority,
                RedirectUri = redirectUri,
            // PostLogoutRedirectUri is the page that users will be redirected to after sign-out. In this case, it is using the home page
            PostLogoutRedirectUri = redirectUri,
                Scope = OpenIdConnectScope.OpenIdProfile,
            // ResponseType is set to request the id_token - which contains basic information about the signed-in user
            ResponseType = OpenIdConnectResponseType.IdToken,
            // ValidateIssuer set to false to allow personal and work accounts from any organization to sign in to your application
            // To only allow users from a single organizations, set ValidateIssuer to true and 'tenant' setting in web.config to the tenant name
            // To allow users from only a list of specific organizations, set ValidateIssuer to true and use ValidIssuers parameter
            TokenValidationParameters = new TokenValidationParameters()
                {
                    ValidateIssuer = false // This is a simplification
            },
            // OpenIdConnectAuthenticationNotifications configures OWIN to send notification of failed authentications to OnAuthenticationFailed method
            Notifications = new OpenIdConnectAuthenticationNotifications
                {
                    AuthenticationFailed = OnAuthenticationFailed,
                    MessageReceived = OnMessageReceived
                }
            }
        );
    }

    /// <summary>
    /// Handle failed authentication requests by redirecting the user to the home page with an error in the query string
    /// </summary>
    /// <param name="context"></param>
    /// <returns></returns>
    private Task OnAuthenticationFailed(AuthenticationFailedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> context)
    {
        context.HandleResponse();
        context.Response.Redirect("/?errormessage=" + context.Exception.Message);
        return Task.FromResult(0);
    }

    private Task OnMessageReceived(MessageReceivedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
    {
        string tmp = notification.ProtocolMessage.ErrorDescription;
        return Task.FromResult(0);
    }
}

This code does not work unless I enable implicit flow in Azure AD. I don't want to use implicit flow because of security reasons. I would rather use authorization flow. What changes do I need to make, so that this code will work without enable implicit flow in Azure?

Answer 1

According to your code, you use OpenID Connect protocol to integrate Azure AD auth in your application. If so, the app registration in the AD portal must have the implicit grant of id_tokens enabled in the Authentication tab (which sets the oauth2AllowIdTokenImplicitFlow flag in the application manifest to true). So that users can successfully request an ID token from the /authorization endpoint. If we do not do that, we will get the unsupported_response error. For more details, please refer to here.