[vinceve]

What about error representation? Most of the time I find that actually representing errors is the hard part of creating a REST api.

You usually want some representation of each field, plus maybe a generic one. I always have troubles with this. Is there a standard or a proper way to define/do this? I would be very interested.

[idbehold]

There's an RFC for that! https://tools.ietf.org/html/rfc7807

[3pt14159]

If you are returning multiple errors of different types, (403 for the forbidden change and 422 for the incorrectly set field) then you are supposed to role it up into a generic 400. Google JSON API for more information about the right way to represent multiple errors at a time.