> Bilateral with whom?

That's very subjective. It's also not a matter of permissions, as we are talking about sovereign states here. Aside from the rational arguments for or against the war, the relational issues of loyalty and solidarity were also present in this case.
It was a very soothing fact that by the time Germany decided to cut some substantial ties with the USA, only the UK and the governments of Spain and Australia were in favor of the Americans and their politics. So, it could be said that a large, international consensus was indeed achieved with Germany saying no to the war in Iraq (whilst it shouldn't be forgotten that they had been saying yes to the war against Yugoslavia a few years prior). But it's my subjective opinion that the current international community has been in very poor shape and has made very poor decisions in the recent past, most notably the UN.