Microsoft.AspNetCore.Authentication.AzureAD.UI throws OptionsValidationException: The 'Instance' option must be provided, if there is another Cookies authentication

[vbornand]

Describe the bug

Adding Azure AD Authentication fails if it is not the default authentication scheme.

The PR #9967 from @mderriey seems the cause of this issue.

To Reproduce

Steps to reproduce the behavior:

1. Create a new ASP.NET Core Web Application project:

• ASP.NET Core 3.0
• Empty template (Source: .NET Core 3.0.0-preview8-013656)
• No Authentication

2. Add the NuGet package Microsoft.AspNetCore.Authentication.AzureAD.UI Version 3.0.0-preview8.19405.7
3. Add the using: using Microsoft.AspNetCore.Authentication;
4. Add the following code in ConfigureServices method:

services.AddAuthentication(Microsoft.AspNetCore.Authentication.Cookies.CookieAuthenticationDefaults.AuthenticationScheme)
.AddCookie()
.AddAzureAD(options =>
{
  options.Instance = "https://login.microsoftonline.com/";
  options.Domain = "tenant.com";
  options.TenantId = "bb7d68f5-f0df-47ba-9c68-8158c5ae67f3";
  options.ClientId = "794df22f-196a-4b5e-9bd8-cbc5015e6c7d";
  options.CallbackPath = "/signin-oidc";
});

5. Add app.UseAuthentication(); in the Configure method, after the app.UseRouting(); line.
6. Start the application
7. See error:

Microsoft.Extensions.Options.OptionsValidationException: The 'Instance' option must be provided.
   at Microsoft.Extensions.Options.OptionsFactory`1.Create(String name)
   at Microsoft.Extensions.Options.OptionsMonitor`1.<>c__DisplayClass11_0.<Get>b__0()
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.get_Value()
   at Microsoft.Extensions.Options.OptionsCache`1.GetOrAdd(String name, Func`1 createOptions)
   at Microsoft.Extensions.Options.OptionsMonitor`1.Get(String name)
   at Microsoft.AspNetCore.Authentication.AzureAD.UI.AzureADCookieOptionsConfiguration.Configure(String name, CookieAuthenticationOptions options)
   at Microsoft.Extensions.Options.OptionsFactory`1.Create(String name)
   at Microsoft.Extensions.Options.OptionsMonitor`1.<>c__DisplayClass11_0.<Get>b__0()
   at System.Lazy`1.ViaFactory(LazyThreadSafetyMode mode)
   at System.Lazy`1.ExecutionAndPublication(LazyHelper executionAndPublication, Boolean useDefaultConstructor)
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.get_Value()
   at Microsoft.Extensions.Options.OptionsCache`1.GetOrAdd(String name, Func`1 createOptions)
   at Microsoft.Extensions.Options.OptionsMonitor`1.Get(String name)
   at Microsoft.AspNetCore.Authentication.AuthenticationHandler`1.InitializeAsync(AuthenticationScheme scheme, HttpContext context)
   at Microsoft.AspNetCore.Authentication.AuthenticationHandlerProvider.GetHandlerAsync(HttpContext context, String authenticationScheme)
   at Microsoft.AspNetCore.Authentication.AuthenticationService.AuthenticateAsync(HttpContext context, String scheme)
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Routing.EndpointRoutingMiddleware.SetRoutingAndContinue(HttpContext httpContext)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

Expected behavior

No error

Additional context

.NET Core SDK (reflecting any global.json):
Version: 3.0.100-preview8-013656
Commit: 8bf06ffc8d

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18362
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\3.0.100-preview8-013656\

Host (useful for support):
Version: 3.0.0-preview8-28405-07
Commit: d01b2fb7bc

.NET Core SDKs installed:
2.1.602 [C:\Program Files\dotnet\sdk]
2.1.604 [C:\Program Files\dotnet\sdk]
2.1.700 [C:\Program Files\dotnet\sdk]
2.1.801 [C:\Program Files\dotnet\sdk]
2.2.401 [C:\Program Files\dotnet\sdk]
3.0.100-preview8-013656 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
Microsoft.AspNetCore.All 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.All 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
Microsoft.AspNetCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.0.0-preview8.19405.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 2.1.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.1.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 2.2.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.0.0-preview8-28405-07 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.0.0-preview8-28405-07 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[vbornand]

If another Cookie scheme is added, the AzureADCookieOptionsConfiguration is called for it, but it don't find the AzureADScheme linked to this other cookie scheme. It's logic because this other cookie scheme is not used by AzureADUI. So the method GetAzureADScheme(name) returns null.
It is correct, but when we try to get the AzureADOptions with the named options null we get a not initialized instance of AzureADOptions with the Instance property empty so the validation failed.

I provided a PR to don't try to get the AzureADOptions if the AzureADScheme is null.

For information, I found this bug when I was trying to add Azure AD as external provider with IdentityServer4.

[blowdart]

@Tratcher could you take a look please?