The first two can be used if the document is a building contract. Principal can be used in other contracts, documents, not related to construction
Source:
Onroerend Goed Lexicon/The Property Lexicon, Dutch-English, by A. van den End

Alle door collega's genoemde vertalingen zijn volkomen correct en worden als zodanig bevestigd door alle woordenboeken, Babylon, Google and the like.
Ingeval uit de eerdere of verdere samenhang de 'opdrachtgever' nader bekend is of omschreven kan worden, verdient een minder letterlijke vertaling door middel van een omschrijving meestal de voorkeur.
Bijv.:
The Council/Board (of Directors)/Local Authority/Committee
(has) *commissioned the architect to build the hospital*
Alternatives (depending on context, not my preference as far as I can see in this case) for 'commissioned' are 'contracted' and 'assigned'.
Confirmation of these constructions are found in Grote van Dale, Juridisch Lexicon and de Keizer's Financieel Economisch Lexicon.
Further references upon request.

Veel succes!

dit zou in jouw context kunnen passen. zie:
http://www.csid.ie/tend/arch_pan.html :
..The Awarding Authority wishes to select two panels of architectural practices from which a practice may be chosen or nominated to provide architectural design and co-ordination services for one or more projects as part of a Public/Private Partnership procurement process for Sports Campus Ireland..
of ook wel:
http://www.genconbd.state.al.us/_OLD_STUFF/2k1-code.html :
AWARDING AUTHORITIES

It is the duty of the awarding authority to ascertain if a contractor is duly licensed before permitting him to submit a bid or offer to construct a project involving fifty thousand or more ($5,000 for swimming pool contractors). All architects, engineers and awarding authorities shall include notification in their bid..