Hi, just a disclaimer as I've never used Minio in a serious/professional project, only in home fiddling and school projects, so I may not suggest the optimal way to do things.
You can create Access Keys (Service Accounts) in Minio for your application, and make the bucket(s) accessible only by this account (private with an access policy, I guess). In your JS app, if I remember correctly, you should be able to specify an access key to use for the connection.
Access keys are credentials, so be sure to store them (and pass them around) safely.
I hope this gives you at least a general direction to investigate, happy tinkering!
It seems that feature is not yet implemented, but maybe someone will start working on it
Source: https://github.com/aeharding/wefwef/issues/114