def get_x_mitre(objects, object_type="course-of-action"):
    """return a list of all x_mitre_ properties defined on the given type"""
    keys = set()
    for obj in objects:
        if obj["type"] != object_type:
            # skip any objects that do not match the type
            continue
        for key in obj:
            if key.startswith("x_mitre_"):
                keys.add(key)
    return keys