Richard,

The solution is to implement some simple switch logic in your Metadata Adapter. In other words, the Metadata Adapter is physically one, but based on the item names (thus, on the Data Adapter), it can delegate the actual logic to different classes.

Of course, the authentication logic should be independent of the Data Adapter. It's only the authorization logic that can be switched based in the Data Adapter.

Does this meet your needs?

Cheers

Alessandro