Sender Vouches Issues & Alternative Use Cases

[Mike Tran <mttran@gmail.com>]

Please excuse this question if it has already been posted...

I am looking to see if there is any mechanism in SAML that provides  
assurances to a relying party that the subject of a sender vouches  
saml assertion did in fact provide the asserting party authority to  
make a web service invocation on its behalf.  In addition, I was  
wondering if there is any information on other web service chaining  
use cases that does not utilize sender vouches to propagate identity?

Thanks in advance.

-Mike