Add AuthorizationServerId to example

Required in order to support Okta orgs without a "default" issuer

Author: bdemers

samples-aspnetcore-3x/okta-hosted-login/okta-aspnetcore-mvc-example/Startup.cs

@@ -36,7 +36,8 @@ public void ConfigureServices(IServiceCollection services)
            .AddOktaMvc(new OktaMvcOptions
            {
                 // Replace these values with your Okta configuration
-                OktaDomain = Configuration.GetValue<string>("Okta:OktaDomain"),
+               OktaDomain = Configuration.GetValue<string>("Okta:OktaDomain"),
+               AuthorizationServerId = Configuration.GetValue<string>("Okta:AuthorizationServerId", "default"),
                ClientId = Configuration.GetValue<string>("Okta:ClientId"),
                ClientSecret = Configuration.GetValue<string>("Okta:ClientSecret"),
                Scope = new List<string> { "openid", "profile", "email" },