Geneva Server's Identifier

If you open the Geneva Server MMC, right-click the root node in the treeview, and select Service Properties, you'll be presented with this dialog:



What is meant by that Identifier field?  What does it do and what is it for?  I wondered that too, and Hervey Wilson of the Geneva team told me that it has these two purposes:

• When Geneva Server is in the identity provider role, this identifier is the Issuer URI of the STS which get included in tokens issued by it.
• When Geneva Server is in the federation provider role, this ID is the audience URI that the STS will accept tokens with.