<PackageReference Include="System.ComponentModel.Annotations" Version="5.0.0-preview.7.20364.11" />

System.ComponentModel.DataAnnotations.CustomValidationAttribute

Specifies a custom validation method that is used to validate a property or class instance.
namespace System.ComponentModel.DataAnnotations { public sealed class CustomValidationAttribute : ValidationAttribute { public Type ValidatorType { get; } public string Method { get; } public CustomValidationAttribute(Type validatorType, string method); } }