There is an order for the manufacture of iOS applications. The customer offers to work with the network API that is written by other people for their services, in particular the mobile application. With the help of a proxy, it was possible to establish the full API structure, including checking for the type of client (it is very simple). That is, technically - the ability to use this API is. Interested in the legal aspects of this issue. Is the API legally protected, or is connecting to someone else's API illegal?
Ps. I don’t really like this idea at least because changing the API will cause problems in the current product, but the question is only about the legal side. Thank you