SameSite Cookie attribute ommited by ASP.NET Core
It looks like the issue is that while the SameSite
Enum has a None
value that's interpreted as the default value of simply not providing a SameSite
attribute. You can see this in the code for SetCookieHeaderValue
which only has token values for Strict
and Lax
.
To set a SameSite=None; Secure
cookie you should send the Set-Cookie
header yourself.
(Side note: I'll try to sort out a pull request for the core to add proper None
support)
The issue is now fixed with latest release of .NET Framework and .NET Core.
As I already posted in this other post https://stackoverflow.com/a/58998232/906046, the cookie options SameSiteMode.None
is now working as intended.
For anyone that may need a side-loaded option, I've written, tested, and released a simple solution which plugs into the IIS HTTP request pipeline as an IHttpModule
. The solution basically adds the cookie twice: one with SameSite, once without. This provides 100% browser compatibility as the browsers that understand SameSite=None; Secure use that one while the browsers that do not understand it will use the normal cookie. This is a solution originally proposed by Google themselves and implemented by Auth0 for their product (in a different form).
The gist of the code is below:
using System;
using System.Linq;
using System.Web;
namespace SameSiteHttpModule
{
public class SameSiteDoomsdayModule : IHttpModule
{
/// <summary>
/// Set up the event handlers.
/// </summary>
public void Init(HttpApplication context)
{
// This one is the OUTBOUND side; we add the extra cookie
context.PreSendRequestHeaders += OnEndRequest;
// This one is the INBOUND side; we coalesce the cookies.
context.BeginRequest += OnBeginRequest;
}
/// <summary>
/// The OUTBOUND LEG; we add the extra cookie.
/// </summary>
private void OnEndRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
HttpContext context = application.Context;
// IF NEEDED: Add URL filter here
for (int i = 0; i < context.Response.Cookies.Count; i++)
{
HttpCookie responseCookie = context.Response.Cookies[i];
context.Response.Headers.Add("Set-Cookie", $"{responseCookie.Name}-same-site={responseCookie.Value};SameSite=None; Secure");
}
}
/// <summary>
/// The INBOUND LEG; we coalesce the cookies.
/// </summary>
private void OnBeginRequest(object sender, EventArgs e)
{
HttpApplication application = (HttpApplication)sender;
HttpContext context = application.Context;
// IF NEEDED: Add URL filter here
string[] keys = context.Request.Cookies.AllKeys;
for (int i = 0; i < context.Request.Cookies.Count; i++)
{
HttpCookie inboundCookie = context.Request.Cookies[i];
if (!inboundCookie.Name.Contains("-same-site"))
{
continue; // Not interested in this cookie.
}
// Check to see if we have a root cookie without the -same-site
string actualName = inboundCookie.Name.Replace("-same-site", string.Empty);
if (keys.Contains(actualName))
{
continue; // We have the actual key, so we are OK; just continue.
}
// We don't have the actual name, so we need to inject it as if it were the original
// https://support.microsoft.com/en-us/help/2666571/cookies-added-by-a-managed-httpmodule-are-not-available-to-native-ihtt
// HttpCookie expectedCookie = new HttpCookie(actualName, inboundCookie.Value);
context.Request.Headers.Add("Cookie", $"{actualName}={inboundCookie.Value}");
}
}
public void Dispose()
{
}
}
}
This gets installed like any other HTTP module:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<system.webServer>
<modules>
<add type="SameSiteHttpModule.SameSiteDoomsdayModule, SameSiteHttpModule" name="SameSiteDoomsdayModule"/>
</modules>
<handlers>
<add name="aspNetCore" path="*" verb="*" modules="AspNetCoreModule" resourceType="Unspecified" />
</handlers>
<aspNetCore processPath=".\IC.He.IdentityServices.exe" arguments="" forwardWindowsAuthToken="false" requestTimeout="00:10:00" stdoutLogEnabled="false" stdoutLogFile=".\logs\stdout" />
</system.webServer>
</configuration>
You can find more info here: https://charliedigital.com/2020/01/22/adventures-in-single-sign-on-samesite-doomsday/
It will provide the fix for ANY .NET version, ANY .NET Core version, ANY scenario whether you own the original source code or not.