Your configuration is passed down to the provider. (e.g: new AWS.S3(config)). You can see the complete list of options here
See the using a provider documentation for information on installing and using a provider. And see the environment variables for setting and using environment variables in your configs.
Example
./config/plugins.js
module.exports = ({ env }) => ({
// ...
upload: {
provider: 'aws-s3',
providerOptions: {
accessKeyId: env('AWS_ACCESS_KEY_ID'),
secretAccessKey: env('AWS_ACCESS_SECRET'),
region: env('AWS_REGION'),
params: {
Bucket: env('AWS_BUCKET'),
},
},
},
// ...
});