Use of with CXF STS

Hello -

I am trying to stand up an STS using CXF 2.7.7, and am having trouble with
RST's containing wst:Participants. I have a requirement that, when the RST
contains one or more Participants, each Participant must be added into the
issued token's audience restrictions. The trouble is, the CXF STS doesn't
appear to understand <wst:Participants>.

When I send a token having the form:

<wst:RequestSecurityToken>
<wst:RequestType>http://docs.oasis-open.org/ws-sx/ws-trust/200512/Issue
</wstRequestType>
<wsp:AppliesTo>...</wsp:AppliesTo>
<wst:UseKey>...</wst:UseKey>
<wst:Participants>...</wst:Participants>
</wst:RequestSecurityToken>

I get a "BadRequest" SOAP fault, with the warning "An unknown (DOM)
element was received: Participants" showing up in the catalina log. Is
there a property, bean, or parameter I can use to turn on Participants
processing? Or, will I have to write a custom RequestParser class and hook
it into a custom TokenIssueOperation class? Has anyone done this already?

Thanx,

Steve Chappell