Don't use a the query string normalizer to transform the body

Scenario:
I want to communicate with a JSON API. I want to do a post request with a JSON body and for this I want to pass a hash into the body.

class Abc
  include HTTParty
  format :json
....
  def self.authorize
    r = post('/auth/local', body: { email: username, password: password })
  end
end

What happens is, that this hash, instead of being serialized into a json-string, it is parsed into a query string.
https://github.com/jnunemaker/httparty/blob/master/lib/httparty/request.rb#L167

Instead, I would like to specify a Proc/Class/whatever, like for the query string normalizer, but for the body payload, in order to process the value that I passed for the body into the post method.

Also, generally it makes sense to expect a Hash in the body of a request when dealing with a JSON API. Here's a monkeypatch that enables this and makes the above example work (in Ruby on Rails). It transforms the body automatically when the format is set accordingly:

require 'httparty'

module HTTParty
  module ClassMethods

    private

    def perform_request(http_method, path, options, &block)
      options = ModuleInheritableAttributes.hash_deep_dup(default_options).merge(options)
      process_headers(options)
      process_body(options) # This line was added
      process_cookies(options)
      Request.new(http_method, path, options).perform(&block)
    end

    def process_body(options)
      return unless options[:body]

      if (options[:format] == :json) and options[:body].respond_to?(:to_json)
        options[:body] = options[:body].to_json # Ruby on Rails specific, converts a Hash into a JSON-String
      end
    end

  end

end

Start in lib/httparty/request.rb at the body handling around line 167, then trace the request path used by perform_request and the format option. Compare the existing query-string normalization with the issue's process_body example. Done means JSON API requests can pass a Hash body without it being converted to a query string, while other body formats retain their expected behavior.