Classical server-client architectures implement classical centralised access-control. The problem with that is that administrator with root access has full control over it what may represent unacceptable risk in some scenarios. There are multiple decentralised systems that do not have root administrators - like BitTorrent or Bitcoin (or Ethereum). However, none of them seem to have access control functionality in them. Are there systems that do (but are decentralised)?
Use MFA and split the authentication pieces between separate parties or several pieces of information required to generate a hash used as a password.
Someone who wants access requires the two pieces much like two keys to open a single door.
Firstly, the (partial) answer to the admin problem is Privileged Access Management (PAM). This is typically a bolt-on system that uses higher level processes (perhaps with one or more humans giving authorisation for example) to give temporary privileged access. This is increasingly common and you will certainly find it in use in any global cloud provider.
I'm not so sure about your actual question. I can't think of anything off the top of my head, perhaps others know more.
However, a second possibility that is also increasingly common is to use federated identities. In the past, implementing identity federation was a horribly complex and expensive process. However, with the advent of things like Azure Active Directory and Azure B2B, this is becoming rapidly easier. In this case, you still have central control but of a much smaller "centre" - so, for example, organisations that want to collaborate and share services may confer some level of trust to another organisation.
What you ask can easily be implemented in Ethereum smart contracts, using modifiers. Basically you can build functions in such a way that they can only be called by given addresses. The allowed addresses could be a variable themselves, which may be changed by a user with even higher privileges (with another function with modifiers).