Fix/identity service model validation (#1837)

* Fix indentation

* Fix comment

* Extract ModelStateValidationFilter add to Indentity MVC opts

* Remove unnecessary base constructor call

src/SharedWeb/Utilities/ModelStateValidationFilterAttribute.cs

@@ -0,0 +1,33 @@
+using System.Linq;
+using Bit.Core.Models.Api;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Filters;
+
+namespace Bit.SharedWeb.Utilities
+{
+    public class ModelStateValidationFilterAttribute : ActionFilterAttribute
+    {
+        public ModelStateValidationFilterAttribute()
+        {
+        }
+
+        public override void OnActionExecuting(ActionExecutingContext context)
+        {
+            var model = context.ActionArguments.FirstOrDefault(a => a.Key == "model");
+            if (model.Key == "model" && model.Value == null)
+            {
+                context.ModelState.AddModelError(string.Empty, "Body is empty.");
+            }
+
+            if (!context.ModelState.IsValid)
+            {
+                OnModelStateInvalid(context);
+            }
+        }
+
+        protected virtual void OnModelStateInvalid(ActionExecutingContext context)
+        {
+            context.Result = new BadRequestObjectResult(new ErrorResponseModel(context.ModelState));
+        }
+    }
+}