bitwarden/src/Core/Utilities/SecurityHeadersMiddleware.cs

using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Primitives;

namespace Bit.Core.Utilities
{
    public sealed class SecurityHeadersMiddleware
    {
        private readonly RequestDelegate _next;

        public SecurityHeadersMiddleware(RequestDelegate next)
        {
            _next = next;
        }

        public Task Invoke(HttpContext context)
        {
            // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
            context.Response.Headers.Add("x-frame-options", new StringValues("SAMEORIGIN"));

            // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-XSS-Protection
            context.Response.Headers.Add("x-xss-protection", new StringValues("1; mode=block"));

            // https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
            context.Response.Headers.Add("x-content-type-options", new StringValues("nosniff"));

            return _next(context);
        }
    }
}