Hi, welcome to the forum 
If I’m understanding correctly, you want to send different credentials to authenticate each VU with your service.
If you don’t need static and previously registered credentials, you could generate them at runtime using Math.random(), or if you need something more sophisticated using faker.js. You can either load it directly or bundle it with Webpack.
If you do need static credentials, you can create a JSON file with all of them and then use this approach to select a unique record per VU. In this case be mindful of your memory usage and if the JSON file is large consider using SharedArray.