Comment by ivan_gammel

Maybe you should reconsider the way you ask questions on this forum. Your tone is not appropriate and the question itself just demonstrates that you don't understand this topic.

Yes, I'm aware of this header and know the web standards well enough.

In hypermedia API you communicate to client the list of all operations in the context of the resource (note: not ON the resource), which includes not only basic CRUD but also operations on adjacent resources (e.g. on user account you may have an operation of sending a message to this user). Yes, in theory one could use OPTIONS with a non-standard response body to communicate such operations that cannot be expressed in plain HTTP verbs in Allow header.

However such solution is not practical, because it requires an extra round trip for every resource. There's a better alternative, which is to provide the list of operations with the resource using one of the common standards - HAL, JSON-LD, Siren etc. The example in my another comment in this thread is based on HAL. If you wonder what is that, look no further than at Spring - it does support HAL APIs out of the box from quite a long time. And of course there's an RFC draft and a Wikipedia article (https://en.wikipedia.org/wiki/Hypertext_Application_Language).