def signature_base
      parts = [normalized_request_method, base_string_uri, normalized_request_params_string]
      parts.map { |v| OAuthenticator.escape(v) }.join('&')
    end
def signature_base
      parts = [normalized_request_method, base_string_uri, normalized_request_params_string]
      parts.map { |v| OAuthenticator.escape(v) }.join('&')
    end
signature base string for signing. section 3.4.1

 @return [String]