You should realize that the process is not perfect, that it has changed over the decades, often in response to perceived abuses of the system by various administrations, and because the various Intelligence agencies believe that they have been used by various Administrations and then allowed to hang.
You should also realize that almost all Intelligence activities have at their core the violation of someone's law, generally speaking, just not US law. And yes, this is a tricky point in international relations, one that, upon examination, could make one wonder to what extent nations respect international law and to what extent they just pay lip service to it and invoke it when it is convenient to do so.
What Wikipedia should be saying here is that while black operations do not have normal Congressional oversight, they do have a process of approval that has been approved by Congress and the courts, and that these operations are therefore, in general, believed to be legal activities of the US Government, although by definition they are not ones that they would want to be publicly disclosed.
In other words, the paranoid interpretation that all secret intelligence operations by this country are illegal and not approved by the government is simply not true.
But that said, or at least that is my understanding, do I really want to try and change Wikipedia?