Prebid Server supports Private MarketPlace deals in this way:
seatbid.bid.dealid. All bids are returned to the client and the deal can pulled from
ext.prebid.targeting.includewinnersoption is on, then the
hb_dealtargeting value will contain the winning deal ID.
ext.prebid.targeting.includebidderkeysis on, then the
hb_deal_BIDDERtargeting value will contain that deal ID
Ad server line items should be targeted to
hb_deal_BIDDER (for sendAllBids)
hb_deal (for sendTopBid).
Currently Prebid Server doesn’t support the option of preferring deals over open market bids, though a PreferDeals flag is being considered.