Enhancement: S3 backend: accept AWS_SESSION_TOKEN Before, it was not possible to use s3 backend with AWS temporary security credentials(with AWS_SESSION_TOKEN). This change gives higher priority to credentials.EnvAWS credentials provider. https://github.com/restic/restic/issues/1477 https://github.com/restic/restic/pull/1479 https://github.com/restic/restic/pull/1647