def METHOD_NAME(session):
    # For a service to be marked as preview, it must be in the
    # [preview] section and it must have a value of 'true'
    # (case insensitive).
    allowed = []
    preview_services = session.full_config.get('preview', {})
    for preview, value in preview_services.items():
        if value == 'true':
            allowed.append(preview)
    return allowed