Fix AzureAd options validation

[JunTaoLuo]

Addresses #20136

Description

Originally #9967 added options validation for AzureAd auth options, but it introduced a regression where it would throw for other cookie or jwt auth providers.
#13480 fixed this for jwt and cookies auth but the issue also affects OIDC auth. This PR applies the same fix to OIDC auth.

Customer Impact

Customers may not be able to use AzureAd auth combine with other kinds of auth in one app.

Regression?

Yes this is a regression in 3.1

Risk

Low, just adding a null check.

[ghost]

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[AleksandrAlbert]

Hi, I'm still having this issue with 3.1.5

services.AddAuthentication()
              .AddAzureAD(options => Configuration.Bind("AzureAD", options))
              .AddOpenIdConnect("PingOne", "PingOne ID", options =>{...});
                  
services.Configure<OpenIdConnectOptions>(AzureADDefaults.OpenIdScheme, options =>
            {
                options.Authority = options.Authority + "/v2.0/";
                options.TokenValidationParameters.ValidateIssuer = true;
                options.SignInScheme = IdentityConstants.ExternalScheme;
                options.GetClaimsFromUserInfoEndpoint = true;
            });

Throws OptionsValidationException: The 'Instance' option must be provided

My settings for ref:

"AzureAD": {
    "Instance": "https://login.microsoftonline.com/",
    "Domain": "xxx",
    "TenantId": "xxx",
    "ClientId": "xxx",
    "CallbackPath": "/signin-oidc"
  }

[JunTaoLuo]

This fix has not been merged yet. It will be applied to the next 3.1 release (3.1.7).

[AleksandrAlbert]

Ok thank you, is there a scheduled release date?

[JunTaoLuo]

It will be out in approximately a month. Generally we don't give out specific dates: see https://github.com/dotnet/core/blob/master/roadmap.md#upcoming-ship-dates.