Add a fluent Validate overload for adding validator types

src/libraries/Microsoft.Extensions.Options/ref/Microsoft.Extensions.Options.cs

@@ -171,6 +171,7 @@ public OptionsBuilder(Microsoft.Extensions.DependencyInjection.IServiceCollectio
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3>(System.Action<TOptions, TDep1, TDep2, TDep3> configureOptions) where TDep1 : class where TDep2 : class where TDep3 : class { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3, TDep4>(System.Action<TOptions, TDep1, TDep2, TDep3, TDep4> configureOptions) where TDep1 : class where TDep2 : class where TDep3 : class where TDep4 : class { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3, TDep4, TDep5>(System.Action<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> configureOptions) where TDep1 : class where TDep2 : class where TDep3 : class where TDep4 : class where TDep5 : class { throw null; }
+        public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembers(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] TValidateOptions>() where TValidateOptions : class, Microsoft.Extensions.Options.IValidateOptions<TOptions> { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate(System.Func<TOptions, bool> validation) { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate(System.Func<TOptions, bool> validation, string failureMessage) { throw null; }
         public virtual Microsoft.Extensions.Options.OptionsBuilder<TOptions> Validate<TDep>(System.Func<TOptions, TDep, bool> validation) where TDep : notnull { throw null; }

src/libraries/Microsoft.Extensions.Options/src/OptionsBuilder.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.Extensions.Options
@@ -335,6 +336,18 @@ public virtual OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3, TDep4
             return this;
         }
 
+        /// <summary>
+        /// Registers an <see cref="IValidateOptions{TOptions}"/> type for an options type.
+        /// </summary>
+        /// <typeparam name="TValidateOptions">The validation type.</typeparam>
+        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
+        public virtual OptionsBuilder<TOptions> Validate<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] TValidateOptions>()
+            where TValidateOptions : class, IValidateOptions<TOptions>
+        {
+            Services.AddTransient<IValidateOptions<TOptions>, TValidateOptions>();
+            return this;
+        }
+
         /// <summary>
         /// Registers a validation action for an options type using a default failure message.
         /// </summary>

src/libraries/Microsoft.Extensions.Options/tests/Microsoft.Extensions.Options.Tests/OptionsBuilderTest.cs

@@ -814,5 +814,34 @@ public void ValidateOnStart_ConfigureBasedOnDataAnnotationRestrictions_Validatio
 
             Assert.NotNull(value);
         }
+
+        [Fact]
+        public void ValidateWithValidatorType_ValidatesFailureCorrectly()
+        {
+            var services = new ServiceCollection();
+            services.AddOptions<ComplexOptions>()
+                .Configure(o => o.Boolean = false)
+                .Validate<ComplexOptionsValidator>();
+
+            var sp = services.BuildServiceProvider();
+
+            var error = Assert.Throws<OptionsValidationException>(() => sp.GetRequiredService<IOptions<ComplexOptions>>().Value);
+            ValidateFailure<ComplexOptions>(error, Options.DefaultName, 1, "Boolean != true");
+        }
+
+        [Fact]
+        public void ValidateWithValidatorType_ValidationSuccessful()
+        {
+            var services = new ServiceCollection();
+            services.AddOptions<ComplexOptions>()
+                .Configure(o => o.Boolean = true)
+                .Validate<ComplexOptionsValidator>();
+
+            var sp = services.BuildServiceProvider();
+
+            var value = sp.GetRequiredService<IOptions<ComplexOptions>>().Value;
+
+            Assert.NotNull(value);
+        }
     }
 }