Ensure AzureADOptions.Instance is set

src/Azure/AzureAD/Authentication.AzureAD.UI/src/AzureADAuthenticationBuilderExtensions.cs

@@ -60,6 +60,8 @@ public static AuthenticationBuilder AddAzureADBearer(
 
             builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<AzureADOptions>, AzureADOptionsConfiguration>());
 
+            builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IValidateOptions<AzureADOptions>, AzureADOptionsValidation>());
+
             builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<JwtBearerOptions>, AzureADJwtBearerOptionsConfiguration>());
 
             builder.Services.Configure(scheme, configureOptions);
@@ -115,6 +117,8 @@ public static AuthenticationBuilder AddAzureAD(
 
             builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<AzureADOptions>, AzureADOptionsConfiguration>());
 
+            builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IValidateOptions<AzureADOptions>, AzureADOptionsValidation>());
+
             builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<OpenIdConnectOptions>, AzureADOpenIdConnectOptionsConfiguration>());
 
             builder.Services.TryAddEnumerable(ServiceDescriptor.Singleton<IConfigureOptions<CookieAuthenticationOptions>, AzureADCookieOptionsConfiguration>());

src/Azure/AzureAD/Authentication.AzureAD.UI/src/AzureADOptionsValidation.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.using Microsoft.AspNetCore.Authorization;
+
+using Microsoft.Extensions.Options;
+
+namespace Microsoft.AspNetCore.Authentication.AzureAD.UI
+{
+    internal class AzureADOptionsValidation : IValidateOptions<AzureADOptions>
+    {
+        public ValidateOptionsResult Validate(string name, AzureADOptions options)
+        {
+            if (string.IsNullOrEmpty(options.Instance))
+            {
+                return ValidateOptionsResult.Fail($"The '{nameof(AzureADOptions.Instance)}' option must be provided.");
+            }
+
+            return ValidateOptionsResult.Success;
+        }
+    }
+}

src/Azure/AzureAD/Authentication.AzureAD.UI/test/AzureADAuthenticationBuilderExtensionsTests.cs

@@ -2,10 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.using Microsoft.AspNetCore.Authorization;
 
 using System;
+using Microsoft.AspNetCore.Authentication.AzureAD.UI;
 using Microsoft.AspNetCore.Authentication.Cookies;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.AspNetCore.Authentication.OpenIdConnect;
-using Microsoft.AspNetCore.Authentication.AzureAD.UI;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
@@ -237,6 +237,28 @@ public void AddAzureAD_ThrowsWhenCookieSchemeIsAlreadyInUse()
             Assert.Equal(expectedMessage, exception.Message);
         }
 
+        [Fact]
+        public void AddAzureAD_ThrowsWhenInstanceIsNotSet()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            services.AddSingleton<ILoggerFactory>(new NullLoggerFactory());
+
+            services.AddAuthentication()
+                .AddAzureAD(o => { });
+
+            var provider = services.BuildServiceProvider();
+            var azureADOptionsMonitor = provider.GetService<IOptionsMonitor<AzureADOptions>>();
+
+            var expectedMessage = "The 'Instance' option must be provided.";
+
+            // Act & Assert
+            var exception = Assert.Throws<OptionsValidationException>(
+                () => azureADOptionsMonitor.Get(AzureADDefaults.AuthenticationScheme));
+
+            Assert.Contains(expectedMessage, exception.Failures);
+        }
+
         [Fact]
         public void AddAzureADBearer_AddsAllAuthenticationHandlers()
         {
@@ -400,5 +422,27 @@ public void AddAzureADBearer_ThrowsWhenBearerSchemeIsAlreadyInUse()
 
             Assert.Equal(expectedMessage, exception.Message);
         }
+
+        [Fact]
+        public void AddAzureADBearer_ThrowsWhenInstanceIsNotSet()
+        {
+            // Arrange
+            var services = new ServiceCollection();
+            services.AddSingleton<ILoggerFactory>(new NullLoggerFactory());
+
+            services.AddAuthentication()
+                .AddAzureADBearer(o => { });
+
+            var provider = services.BuildServiceProvider();
+            var azureADOptionsMonitor = provider.GetService<IOptionsMonitor<AzureADOptions>>();
+
+            var expectedMessage = "The 'Instance' option must be provided.";
+
+            // Act & Assert
+            var exception = Assert.Throws<OptionsValidationException>(
+                () => azureADOptionsMonitor.Get(AzureADDefaults.AuthenticationScheme));
+
+            Assert.Contains(expectedMessage, exception.Failures);
+        }
     }
 }