def auth_headers(auth_token):
    """Return HTTP authentication headers for API requests.

    Kwargs:
        auth_token: valid API token.

    Returns a dict that can be passed into requests.post as the
        'headers' dict.

    """
    assert auth_token is not None, (
        u"No valid HipChat authentication token found.")
    return {
        'Authorization': 'Bearer %s' % auth_token,
        'Host': 'api.hipchat.com',
        'Content-Type': 'application/json'
    }