Link relations can be designed that indicate which HTTP methods are allowed. HAL is heavily dependent on conveying semantics via link relations, which is something that some people don't like doing.

Consider the oauth2-token link relation defined here[1]. The definition of this link relation refers to RFC 6749 [2] which states that it is necessary to pass a application/x-www-form-urlencoded body using POST.

[1] https://tools.ietf.org/html/draft-wmills-oauth-lrdd-07#secti... [2] https://tools.ietf.org/html/rfc6749#section-4.1.3

Formally, they're absolutely right. Information like that is out of band with HAL.

In practice, I deal with it by sticking to HTTP verb conventions and specifying what to do in the documentation.

It's not automatic -- it'd be e.g. rsrc.somelink.post(params) instead of rsrc.somelink(params) in HyperResource's case -- but it works, and any human who knows what the 'somelink' rel is supposed to do might also be expected to know how to use it.