How to add "allow-downloads" to the sandbox attributes list

Question

I am trying to get files from my MVC project (asp.net core 3.1)

I created a link

<a asp-action="@nameof(HomeController.Download)" asp-controller="@HomeController.Name" asp-route-fileName="fileName.doc" download>FileName</a>

I created a controller

public async Task<ActionResult> Download(string fileName) {
            var path = Path.Combine(_hostingEnvironment.WebRootPath, fileName);
            if (!System.IO.File.Exists(path)) {
                return NotFound();
            }

            var fileBytes = await System.IO.File.ReadAllBytesAsync(path);
            var response = new FileContentResult(fileBytes, "application/vnd.openxmlformats-officedocument.wordprocessingml.document") {
                FileDownloadName = fileName
            };
            return response;
        }

In Chrome i get the warning

Download is disallowed. The frame initiating or instantiating the download is sandboxed, but the flag ‘allow-downloads’ is not set. See https://www.chromestatus.com/feature/5706745674465280 for more details.

Following the link, how can i add:

add "allow-downloads" to the sandbox attributes list to opt in

The file is downloaded if i click the button from Microsoft Edge

Answer 1

This is what I had to do for my project, hopefully it will point you to the right direction.

In your Startup.cs

services.AddMvc(options =>{
   options.Filters.Add(new MyActionFilterAttribute());
}

Then in MyActionFilterAttribute.cs

 public class MyActionFilterAttribute : ActionFilterAttribute
        {
            public override void OnResultExecuting(ResultExecutingContext filterContext)
            {
                filterContext.HttpContext.Response.Headers.Add("Content-Security-Policy",  "sandbox allow-downloads; " )
            }
}