How to implement google drive file upload in vuejs client app

Question

I've read this article about google drive implementation in nodejs. I want to give to the users of the app the ability to upload the processed files from the app to their google drive account. The article show how to implement a nodejs solution, but since the server will run on localhost, how I can authorize the user on the client side using vuejs? I've found this question but it's very old and I'm not sure if can really help me at all.

At the moment my nodejs script will save the processed files on the users machine using fs.writeFile.

// espress endpoint
        this.app.post('/processFiles', async (req, res) => {
            for(let file in req.files){
                //console.log(req.files[file]);
                await this.composeData(req.files[file]);
            }
            res.setHeader('Content-Type', 'application/json');
            res.send({processStatus: '', outputPath: this.tmpDir});
        });
// processing file method
    async composetData(file){   
        //some file compression stuff
        this.output = path.format({dir: this.tmpDir, base: file.name});
        await fs.writeFile(this.output, this.processedData);
    }

Since I want to implement a client side solution, I'm thinking to add an endpoint to my express server that will send processed files back so the client code can do the gdrive upload.

//vue app code
        processFiles(){
            const formData = new FormData();
            this.selectedFiles.forEach( (file, i) => {
                formData.append(`file${i}`, file);
            });

            axios({
                method: 'POST',
                url: 'http://localhost:9000/processFiles',
                data: formData
            }).then( (res) => {
    //here i want to implement gdrive upload
                console.log(res);
            });
        }

Can anyone provide me some help about?