How do I configure ASP.Net OutputCache to vary by http vs https?

Question

Here is the scenario, a user opens up non-secure page from our WebApp, let's call it PageA, in their browser and then clicks a link in there that takes them to a secure instance of PageB. Once in PageB the user can subsequently click a link that takes them back to a secure instance of PageA (which they already viewed and is in OutputCache). I observed that even though PageA is being accessed over a different URL after visiting PageB (the secure one) it's actually pulling the prior cached copy rather making a fresh one. I verified this behavior in a debugging session, and was surprised that ASP.Net used the same OutputCache item for a secure copy of the page.

My question is why is it this way? And how do I tell the ASP.Net OutPutCache to treat access from secure URL as a different/unique item than the non-secure equivalent?

[Background]

We recently switched our Web Sites images over to use Scene7/Akamai for all images. As a result of this we added code to use different Scene7 url's when viewing a given page on a secure connection. This OutputCache issue is not allowing for the logic that outputs the secure url's to execute, and is resulting in ugly browser warnings.

Answer 1

I think that you can do a VaryByCustom="scheme" and add this to your Global.asax.cs file (inlcuding a couple other others that I use as well app version & user):

    public override string GetVaryByCustomString(HttpContext context, string custom)
    {
        if (custom.Equals("version", StringComparison.CurrentCultureIgnoreCase))
        {
            Assembly asm = Assembly.GetExecutingAssembly();
            string[] parts = asm.FullName.Split(',');
            string version = parts[1].Trim().ToLower();
            return version;
        }
        else if (custom.Equals("user", StringComparison.CurrentCultureIgnoreCase))
        {
            var user = Membership.Users.CurrentUser;
            return null == user ? string.Empty : user.Id.ToString();
        }
        else if (custom.Equals("scheme", StringComparison.CurrentCultureIgnoreCase))
        {
            var scheme = context.Request.IsSecureConnection ? "https" : "http";
            return scheme;
        }
        else
            return base.GetVaryByCustomString(context, custom);
    }

Answer 2

This doesn't answer the question as worded but it may eliminate your need to vary by scheme. If you are hard coding the "http://" for the Scene7 urls you can change them to scheme-relative urls.

<img src="http://site.scene7.com/images/someimage.jpg" />
=>
<img src="//site.scene7.com/images/someimage.jpg" />

That will cause the browser to automatically ask for the resource with the same scheme as the referring page. That's assuming you have an SSL certificate for your scene7 domain of course.

Answer 3

I've never tried it but you might be able to use the Outputcache VaryByHeader property and the "host" header, which specifies the Internet host and port number of the resource being requested.

The question I'd have is why are you redirecting to PageA over secure after from PageB. If its a non-secure page, couldn't you fix the PageB redirect to always redirect to non-secure.