private function normalize_parameters( $parameters ) {

		$normalized_parameters = array();

		foreach ( $parameters as $key => $value ) {

			// percent symbols (%) must be double-encoded
			$key   = str_replace( '%', '%25', rawurlencode( rawurldecode( $key ) ) );
			$value = str_replace( '%', '%25', rawurlencode( rawurldecode( $value ) ) );

			$normalized_parameters[ $key ] = $value;
		}

		return $normalized_parameters;
	}