Your configuration is passed down to the provider. (e.g: `new AWS.S3(config)`). You can see the complete list of options [here](https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#constructor-property)
See the [using a provider](https://strapi.io/documentation/developer-docs/latest/development/plugins/upload.html#using-a-provider) documentation for information on installing and using a provider. And see the [environment variables](https://strapi.io/documentation/developer-docs/latest/setup-deployment-guides/configurations.html#environment-variables) for setting and using environment variables in your configs.