Show a private RSA key

    CLI Example:

    .. code-block:: bash

        salt-run digicert.show_rsa myminion domain.example.com

def show_rsa(minion_id, dns_name):
    '''
    Show a private RSA key

    CLI Example:

    .. code-block:: bash

        salt-run digicert.show_rsa myminion domain.example.com
    '''
    cache = salt.cache.Cache(__opts__, syspaths.CACHE_DIR)
    bank = 'digicert/domains'
    data = cache.fetch(
        bank, dns_name
    )
    return data['private_key']