The other day and friend of mine asked me about portable STS implementations, if I knew about any available solution that he could use on his company. That reminded me of a conversation I had like two years ago with another developer working on custom .NET CLR framework version for portable devices (like smartcards). As part of that project, his team was also working on a TCP/IP communication stack for the device, and a http handler for accepting raw WS-TRUST messages. One goal for that project was to have a P-STS that could be interoperable with WCF. The idea seemed very promising at time.
So, what is a PSTS after all ?. In a few words, it is a service running on a portable device that exposes WS-TRUST endpoints and can issue security tokens of any kind (e.g, SAML tokens).
Making a search today on google will drop several P-STS products or solutions, some of them also claim to be interoperable with WCF and Microsoft Cardspace V1.
In terms of identity management, A P-STS really makes a great different over existing authentication mechanisms like username/password, X509 certificates or any other kind of two-factor authentication device. Most of these authentication mechanisms are widely accepted and used today in applications within corporate environments or applications that requires off-line support. However, sometimes they lack of a truly identity support, which means that they do not represent the user identity at all in the context of those applications, they are just a way of identifying returning users, or they are hard to extend with additional user's identity claims.
I can not deny that X509 certificates have demonstrated to be a very effective and secure way to authenticate users. In addition, X509 certificates can be extended with some custom attributes, the space is limited, but at least there is a possibility. However, X509 certificates represent hard tokens, the claims stored on a certificate can not be changed once it has been issued. Therefore, they are a good solution as long as their information do not change frequently over a period of time.
Issue tokens (e.g SAML tokens) on other hand are more dynamic and cheaper to create. They usually have a short expiration time, they can issued and used on the fly, but what is more important, they can carry custom information or claims about the subject it has been issued for.
Some good news is that the Geneva Cardspace team has also announced some support for roaming scenarios in Cardspace V2. There will be a way to store our identity cards on a device (or somewhere in the cloud), which will be great to combine with a P-STS, no need to export/import the cards anymore. This scenario was not possible in Cardspace V1, and here is the explanation. According to what Rich Randall mentioned in the PDC talk "BB44 Identity: Windows CardSpace "Geneva" Under the Hood ", the future Cardspace interface could look as follow,
As you can see, it will not be long until we have complete and portable identity solutions for roaming scenarios.