Oh, I'm sure it can be done, and what you're describing sounds quite nice.

All I take issue with is the claim that this is a way to make the unauthorized actions "impossible to utter". The reality is that, at least at some level, you always have to evaluate a request and, based on some cryptography related to user identity, decide if you'll honor it or refuse it. That may be checking a cookie to look up the user and then checking a separate place to see if the user is authorized to perform the action (perhaps with an extra step of finding a role, etc), or it can be checking a "pre-approval" signature obtained at some earlier point as you're describing here, but it's ultimately the same concept, and isn't "implicitly handled" in one case anymore than the other.

I would hate to argue over semantics. But in addition to the keys being checked automatically at run time, the type system ensured that, unless the capability had been revoked, illegal requests would not type-check at compile time. Which I think is pretty close to unutterable.

The keys were there to stop an attacker, the type-checker helps the good guys stay in line.