Overide some class methods and attributes on amz-sp-api gem to allow for grantless operations

amz_sp_api.rb

AmzSpApi::SpApiClient.class_eval do

  def request_lwa_access_token
    newself = self.dup
    newself.config = config.dup
    newself.config.host = 'api.amazon.com'

    data, status_code, headers = newself.super_call_api(:POST, '/auth/o2/token',
      :header_params => {
       'Content-Type' => 'application/x-www-form-urlencoded'
      },
      :form_params =>  {
        grant_type: config.grant_type || 'refresh_token',
        refresh_token: config.refresh_token,
        scope: config.scope,
        client_id: config.client_id,
        client_secret: config.client_secret
      },
      :return_type => 'Object')

    unless data && data[:access_token]
      fail ApiError.new(:code => status_code,
                        :response_headers => headers,
                        :response_body => data)
    end

    data
  end
end

AmzSpApi::SpConfiguration.class_eval do
  attr_accessor :scope
  attr_accessor :grant_type
end

Perfect, I tried this and success to request with grantless APIs. I hope that AmzSpApi merges this.