The APA was enacted by socialist Franklin Roosevelt in an attempt to increase the size of the Federal government as much as possible. This way people could keep inventing agencies that would have unlimited power and budgets and there would be NO judicial review which is a violation of when Marbury LOST to Madison which was in the Declaration of Independents.
It requires such things as notice and hearing, which means you can do whatever you want without notice or hearing. It also does adjudication and rulemaking. That means agencies can make rules and not even be adjudicated. I guess constutionality only matters if your a lib.
The APA is NOT allowed by the Constituition because it is arbitrary and capricious.