The ClaimsManager defined on AbstractOperation holds a list of ClaimsHandler objects. So to support claim handling in the STS, it is necessary to implement one or more ClaimsHandler objects for whatever Claim URIs you wish to support, and register them with a ClaimsManager instance, which will be configured on the TokenIssueOperation object.
As detailed in the previous article, the TokenIssueOperation gets the realm of the current request, and does some processing of the AppliesTo address, after the RequestParser has finished parsing the request. The RequestClaimCollection object that has been constructed by the RequestParser is then processed. For each RequestClaim in the collection, it checks to see whether the ClaimsManager has a ClaimsHandler implementation registered that can "handle" that Claim (by checking the URIs). If it does not, and if the requested claim is not optional, then an exception is thrown.
If a ClaimsHandler implementation is registered with the ClaimsManager that can handle the desired claim, then the claims are passed through to the TokenProvider implementation, which is expected to be able to invoke the relevant ClaimHandler object, and insert the processed Claim into the generated security token. How this is done is entirely up to the user. For example, for the use-case given above of a SAML 1.1 token containing a "role" claim, the user could implement a custom AttributeStatementProvider instance that evaluates the claim values (via a custom ClaimsHandler implementation registered with the ClaimsManager) and constructs a set of Attributes accordingly in an AttributeStatement. An example of how to do this is given in the CXF unit tests.