Duplicity with S3 needs the AWS credentials as env vars

After having the following error while testing Duplicity with a S3-compatible Object Storage service (Scaleway)

NoAuthHandlerFound: No handler was ready to authenticate. 1 handlers were checked. ['HmacAuthV1Handler'] Check your credentials

I tried passing my credentials through environment variables

export AWS_ACCESS_KEY_ID="aws_access_key_id"
export AWS_SECRET_ACCESS_KEY="aws_secret_access_key"

The error didn't appear in the following test and the backup worked well.