Вытащил солюшен на уровень выше, чтобы прощё было дотнетить

ApplicationLayer/Services/AuthServices/Requests/Validation/RegisterRequestValidator.cs

@@ -0,0 +1,17 @@
+using ApplicationLayer.Services.AuthServices.Common;
+using ApplicationLayer.Services.AuthServices.NeededServices;
+using FluentValidation;
+
+namespace ApplicationLayer.Services.AuthServices.Requests.Validation;
+
+public class RegisterRequestValidator : AbstractValidator<RegisterRequest>
+{
+    public RegisterRequestValidator(IUsersRepository users, IValidator<AuthData> authDataValidator)
+    {
+        RuleFor(r => r.AuthData)
+            .NotEmpty()
+            .SetValidator(authDataValidator)
+            .MustAsync(async (authData, ct) => await users.FindByEmailAsync(authData.Email, ct) is null)
+            .WithMessage("Email already exists");
+    }
+}