Comment Can free ICQ clients use ICQ servers, reloaded (Score 3, Interesting) 103
The response of "User-Agent is not authentication" is a strawman response to "Unofficial clients should not use our servers". They used it as identification of clients, not authentication. Would the developers be happier if they had used an API key for the web interaction, but package that fixed API key into the app? Would that be "authentication" and thus better to them? It's the same effect, and the open source clone would copy it too.
Same discussion as 30 years ago with open source clones of messaging apps such as ICQ. The open source client pretends, on those days through reverse engineering, to be the official client. Ultimately, it was okay then, because it was beneficial for the operators to have a larger network of users who can talk to each other. Does this dynamic apply here?