Proxy API requests through e.g. your Middleman to avoid cross domain issues.

config.rb

class APIProxy

  def call(env)
    request = Rack::Request.new(env)
    api_url = request.params['api_url']

    [200, { 'Content-Type' => 'application/json' }, [get_json(api_url)]]
  end

  private

  def get_json(url)
    uri      = URI.parse(URI::unescape(url))
    response = Net::HTTP.get(uri)

    response
  end

end

map '/api_proxy' do
  run APIProxy.new
end