How to use the forge-apis.DerivativesApi function in forge-apis

return (new Promise((fulfill, reject) => {
			if (!fileurn || !modelurn)
				return (reject('Missing the required parameter {urn} when calling getManifest'));
			let ModelDerivative = new ForgeAPI.DerivativesApi();
			ModelDerivative.apiClient.basePath = 'https://otg.autodesk.com';
			ModelDerivative.apiClient.callApi(
				'/modeldata/file/' + fileurn + encodeURI(elt), 'GET',
				{}, { acmsession: modelurn }, { 'Accept-Encoding': 'gzip, deflate', pragma: 'no-cache' },
				{}, null,
				[], ['application/json'], null,
				this._token, this._token.getCredentials()
			)
				.then((res) => {
					return (utils.gunzip(res.body, true));
				})
				.then((data) => {
					return (utils.writeFile(outFile, data, 'binary', true));
				})
				.then((data) => {
					console.log(' >> ', outFile);

router.get ('/translate/:urn/progress', function (req, res) {
	var accessToken =req.query.accessToken ;
	var urn =req.params.urn ;

	var oAuth2 =new ForgeApis.AuthClientTwoLegged ('', '', config.credentials.scope) ;
	oAuth2.setCredentials ({
		access_token: accessToken,
		type: 'Bearer',
		expires_at: 3599,
	}) ;

	var md = new ForgeApis.DerivativesApi();
	md.getManifest (urn, {}, oAuth2, oAuth2.getCredentials ())
		.then (function (data) {
			var name =_path.basename (Buffer.from (data.body.urn, 'base64').toString ()) ;
			if ( data.body.derivatives !== undefined && data.body.derivatives.length > 0 && data.body.derivatives [0].hasOwnProperty ('name') )
				name =data.body.derivatives [0].name ;
			res.json ({
				status: data.body.status,
				progress: data.body.progress,
				urn: data.body.urn,
				name: name
			}).end () ;
			console.log ('Request: ' + data.body.status + ' (' + data.body.progress + ')') ;
		})
		.catch (function (error) {
			res.status (404).end () ;
		}) ;

router.get('/properties', function (req, res) {
    var derivatives = new forgeSDK.DerivativesApi();

    var tokenSession = new token(req.session);

    derivatives.getModelviewProperties(req.query.urn, req.query.guid, {}, tokenSession.getInternalOAuth(), tokenSession.getInternalCredentials())
        .then(function (data) {
            res.json(data.body);
        })
        .catch(function (error) {
            res.status(error.statusCode).end(error.statusMessage);
        });
});

return (new Promise (function (fulfill, reject) {
			let accepted = [ 'application/octet-stream', 'image/png', 'text/html', 'text/css', 'text/javascript', 'application/json' ] ;
			let ModelDerivative =new ForgeAPI.DerivativesApi () ;
			ModelDerivative.apiClient.callApi (
				uri, 'GET',
				{}, {}, {},
				{}, null,
				[], accepted, null,
				//forgeToken.RW, forgeToken.RW.getCredentials ()
				null, null
			)
				//.pipe (zlib.createGunzip ())
				.then ((response) => {
					let body =response.body ;
					if ( ['gzip', 'deflate'].indexOf (response.headers ['content-encoding']) !== -1 )
						body =zlib.gunzipSync (response.body) ;

					if (   response.headers ['content-type'] === 'text/javascript'
						|| response.headers ['content-type'] === 'text/css'

router.get('/metadatas/:urn', function (req, res) {
    var derivatives = new forgeSDK.DerivativesApi();

    var tokenSession = new token(req.session);

    derivatives.getMetadata(req.params.urn, {}, tokenSession.getInternalOAuth(), tokenSession.getInternalCredentials())
        .then(function (data) {
            res.json(data.body);
        })
        .catch(function (error) {
            res.status(error.statusCode).end(error.statusMessage);
        });
});

.then((_oa2legged) => {
				oa2legged = _oa2legged;
				let urn = Forge_MD.createOSSURN(bucketKey, filename, true);
				let md = new ForgeAPI.DerivativesApi();
				return (md.getManifest(urn, {}, oa2legged, oa2legged.getCredentials()));
			})
			.then((manifest) => {

.then((_jobs) => {
				if (_jobs.output.formats.length === 0)
					throw new Error('Please specify an output format');

				let md = new ForgeAPI.DerivativesApi();
				return (md.translate(_jobs, { xAdsForce: force }, oa2legged, oa2legged.getCredentials()));
			})
			.then((response) => {

downloadItem (urn) {
		if (urn === undefined || urn === null)
			return (Promise.reject('Missing the required parameter {urn} when calling getManifest'));
		let ModelDerivative = new ForgeAPI.DerivativesApi();
		return (ModelDerivative.apiClient.callApi(
			'/derivativeservice/v2/derivatives/{urn}', 'GET',
			{ 'urn': urn }, {}, { 'Accept-Encoding': 'gzip, deflate' },
			{}, null,
			[], [], null,
			this._token, this._token.getCredentials()
		));
	}

.then (function (data) {
			//if ( !data.hasOwnProperty ('urn') )
			//	throw new Error ('No URN') ;
			var urn =utils.safeBase64encode (data.objectId) ;
			var ModelDerivative =new ForgeSDK.DerivativesApi () ;
			return (ModelDerivative.getManifest (urn, {}, forgeToken.RW, forgeToken.RW.getCredentials ())) ;
		})
		.then (function (manifest) {