def update_ca_bundle(target=None, source=None, merge_files=None):
    '''
    Update the local CA bundle file from a URL

    .. versionadded:: 2015.5.0

    CLI Example:

    .. code-block:: bash

        salt '*' http.update_ca_bundle
        salt '*' http.update_ca_bundle target=/path/to/cacerts.pem
        salt '*' http.update_ca_bundle source=https://example.com/cacerts.pem

    If the ``target`` is not specified, it will be pulled from the ``ca_cert``
    configuration variable available to the minion. If it cannot be found there,
    it will be placed at ``<<FILE_ROOTS>>/cacerts.pem``.

    If the ``source`` is not specified, it will be pulled from the
    ``ca_cert_url`` configuration variable available to the minion. If it cannot
    be found, it will be downloaded from the cURL website, using an http (not
    https) URL. USING THE DEFAULT URL SHOULD BE AVOIDED!

    ``merge_files`` may also be specified, which includes a string or list of
    strings representing a file or files to be appended to the end of the CA
    bundle, once it is downloaded.

    CLI Example:

    .. code-block:: bash

        salt '*' http.update_ca_bundle merge_files=/path/to/mycert.pem
    '''
    if target is None:
        target = __salt__['config.get']('ca_bundle', None)

    if source is None:
        source = __salt__['config.get']('ca_bundle_url', None)

    return salt.utils.http.update_ca_bundle(
        target, source, __opts__, merge_files
    )