Add validation to RealmCreate

IdentityShroud.Api/Validation/RealmCreateRequestValidator.cs

@@ -0,0 +1,19 @@
+using FluentValidation;
+using IdentityShroud.Core.Messages.Realm;
+
+namespace IdentityShroud.Api.Validation;
+
+public class RealmCreateRequestValidator : AbstractValidator<RealmCreateRequest>
+{
+    private const string SlugPattern = @"^(?=.{1,40}$)[a-z0-9]+(?:-[a-z0-9]+)*$";
+    
+    public RealmCreateRequestValidator()
+    {
+        RuleFor(x => x.Id)
+            .NotEqual(Guid.Empty).When(x => x.Id.HasValue);
+        RuleFor(x => x.Slug)
+            .Matches(SlugPattern).Unless(x => x.Slug is null);
+        RuleFor(x => x.Name)
+            .NotNull().Length(1, 255);
+    }
+}