MVC 5 prevents access to content via Iframe

Question

MVC5 automatically adds the HTTP header X-Frame-Options with SAMEORIGIN. This prevents your site from being loaded into an iframe.

But we can turn this off in Application_Start in the Global.asax.cs.

Example

protected void Application_Start()
{
    AntiForgeryConfig.SuppressXFrameOptionsHeader = true;
}

Update

I have written a post about this MVC5 prevents your website being loaded in an IFRAME

Try something like this in Global.asax:

protected void Application_PreSendRequestHeaders(object sender, EventArgs e)
 {
   HttpContext.Current.Response.Headers.Remove("X-Frame-Options");
 }

EDIT:

Look at answer of Colin Bacon. It is more correct than mine.

In short - don't remove this header if you don't want to run your site in IFRAME because it will open forgery vulnerability. But if you still want to remove it - use AntiForgeryConfig.SuppressXFrameOptionsHeader = true; in Application_Start, it is more cleaner way for doing this.

If you want a little more flexibility, here's an ActionAttribute that adds/removes headers based on a whitelist. If the referrer isn't in the whitelist, then the SAMEORIGIN header is left in place. I was going to paste the code, but SO complains about the length.

https://long2know.com/2016/06/asp-net-anti-forgery-xframe-options/

Here is a replacement Extension method for the HtmlHelper class. It will first clear all X-Frame-Options headers and then add back a single X-Frame-Options header normally added by the built-in AntiForgeryToken method.

This technique respects the SuppressXFrameOptionsHeader setting, but has the downside of removing all previously added X-Frame-Options headers, even those with values other than SAMEORIGIN.

public static MvcHtmlString AntiForgeryTokenSingleHeader(this HtmlHelper html)
{
    string token = AntiForgery.GetHtml().ToString();
    HttpResponseBase httpResponse = html.ViewContext.HttpContext.Response;

    httpResponse.Headers.Remove("X-Frame-Options");
    if (!AntiForgeryConfig.SuppressXFrameOptionsHeader)
    {
        httpResponse.AddHeader("X-Frame-Options", "SAMEORIGIN");
    }
    return new MvcHtmlString(token);
}

Personally, I don't think it's a good idea to disable the X-Frame-Options across the whole site.I've created an ASP.NET MVC filter which removes this header and I simply apply this filter to the portions of the site that are used in iFrames e.g. widgets.

public class AllowDifferentOrigin : ActionFilterAttribute, IActionFilter
{
    public override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        filterContext.HttpContext.Response.Headers.Remove("X-Frame-Options");
        base.OnResultExecuted(filterContext);
    }
}