ASP.net Core Filter to limit allowed Content-Types per method.

LimitContentTypesFilterAttribute.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using System;
using System.Collections.Generic;
using System.Linq;

namespace Stuff.Web
{
    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
    public class LimitContentTypesFilterAttribute : Attribute, IResourceFilter
    {
        private readonly HashSet<string> _allowedContentTypes;

        public LimitContentTypesFilterAttribute(params string[] allowedContentTypes)
        {
            if (allowedContentTypes == null || allowedContentTypes.Length == 0)
            {
                throw new ArgumentException(nameof(allowedContentTypes) + " must not be empty.");
            }

            _allowedContentTypes = new HashSet<string>(allowedContentTypes);
        }

        public void OnResourceExecuted(ResourceExecutedContext context)
        {
        }

        public void OnResourceExecuting(ResourceExecutingContext context)
        {
            var reqContentType = context?.HttpContext?.Request?.ContentType;

            if (string.IsNullOrEmpty(reqContentType)
                || !_allowedContentTypes.Any(ct => string.Equals(ct, reqContentType, StringComparison.OrdinalIgnoreCase)))
            {
                context.Result = new StatusCodeResult(415);
            }
        }
    }
}