Showing how to use ASP.NET Static Assets options to set custom headers on files with Umbraco

StaticAssetsHeaders.cs

using Microsoft.Net.Http.Headers;
using Umbraco.Cms.Core.Composing;

namespace StaticAssets
{
    public class StaticAssetsHeaders : IComposer
    {
        public void Compose(IUmbracoBuilder builder)
        {
            builder.Services.Configure<StaticFileOptions>(options =>
            {
                options.OnPrepareResponse = ctx =>
                {

                    // Need to ignore static assets in Umbraco backoffice
                    // Where the request path starts with umbraco
                    // Example..
                    // /umbraco/lib/font-awesome/css/font-awesome.min.css
                    // /umbraco/js/init.min.js
                    if (ctx.Context.Request.Path.StartsWithSegments("/umbraco"))
                    {
                        return;
                    }


                    // NOTE !!
                    // Images from CMS media pickers that do not use Image Processor will come through here too
                    // <img src="@Model.ImagePicker.Url()" />

                    // Set all static file requests
                    // To have Allow any origin for CORS requests
                    ctx.Context.Response.Headers.Append(HeaderNames.AccessControlAllowOrigin, "*");

                    // Just a custom made up header with a date in
                    ctx.Context.Response.Headers.Append("x-custom-header-date", DateTime.Now.ToString("o"));


                    // Certain file extensions
                    var fileExtension = Path.GetExtension(ctx.File.Name);
                    if (fileExtension == ".svg")
                    {
                        // Set a specific Cache header
                        var typedHeaders = ctx.Context.Response.GetTypedHeaders();

                        // Update or set Cache-Control header
                        var cacheControl = typedHeaders.CacheControl ?? new CacheControlHeaderValue();
                        cacheControl.Public = true;
                        cacheControl.MaxAge = TimeSpan.FromMinutes(1);
                        typedHeaders.CacheControl = cacheControl;
                    }

                    // Other ideas
                    // Add specific cache headers if a static file was served from a specific folder
                    // Such as wwwroot/assets regardless of extension
                };
            });
        }
    }
}