In case you haven't noticed already, Microsoft and others published a number of specifications and an amazing White Paper yesterday all having to do with federating security with Web services.

Although I haven't gone over all the details yet, it is safe to say that this represents an incredible amount of work by Microsoft, IBM, VeriSign, BEA, RSA Security and maybe some others I may have missed.  What impresses me the most is simply the amount of thought and resources put behind this.  This is a big deal folks and I think it is safe to say that integrated, cross-domain security with cross-platform support will be a reality.