Reddit mentions of Build APIs You Won't Hate: Everyone and their dog wants an API, so you should probably learn how to build them.

How do you get a list of all your subscriptions? Why not have a /subscriptions/ endpoint which you can get, post, put and delete to like the articles to manage your subscriptions. If you want an admin user or article author to manage subscriptions to their articles you could also have /articles/1/subscriptions/ or add a filter to the /subscriptions/ endpoint.

As for login - it is not really a resource so does not really have to follow the rest API as strictly. Posting to a login/logout/signup endpoints is fine as these don't tend to get unmanageable and tend to follow different usage patterns in general.

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There are lots of different ways to do things with restful APIs as there is no proper standard but there are a whole bunch of best practices on how to design restful API, most of which say the same things but sometimes contradict each other on the finer details or ignore the more hairy side of designing rest APIs.

Generally, all these have the aim of creating nice usable APIs, so as long as you are able to do that I would say it does not matter so much how the API is designed or if it is completely restful or not. But the best practices are there for a reason and it is worth understanding why if you want to go against them so you know what trade off you are making.

There are quite a few book on the topic such as Build APIs You Won't Hate that are worth a read if you want to get better at API design.