The module has been developed to require IAM Access Key and Secret key.
It should allow the usage of the instance role.
https://github.com/nuxeo/nuxeo-core-binarymanager-cloud/blob/master/nuxeo-core-binarymanager-s3/src/main/java/org/nuxeo/ecm/core/storage/sql/S3DirectBatchHandler.java
It also requires the definition of a role to be passed to the Web-UI.