def normalized_request_params_string
      normalized_request_params.map { |kv| kv.map { |v| OAuthenticator.escape(v) } }.sort.map { |p| p.join('=') }.join('&')
    end
def normalized_request_params_string
      normalized_request_params.map { |kv| kv.map { |v| OAuthenticator.escape(v) } }.sort.map { |p| p.join('=') }.join('&')
    end
section 3.4.1.3.2

 @return [String]