ASP.NET 4 Unleashed

Using Forms Authentication Across Domains

In the previous section, you learned how to share the same authentication cookie across applications located on the same server or a different server. But how do you share the same authentication cookie across domains?

A browser cookie is always domain relative. For example, the Amazon website cannot read cookies set by the Barnes & Noble website, which is a good thing. However, you might discover that you need to share authentication information across websites with different domains.

You can work around this problem by passing an authentication ticket in a query string parameter rather than in a cookie. There is nothing to prevent you from passing query strings between domains.

To enable this scenario, ...