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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def auth_keys(user=None,
              config='.ssh/authorized_keys',
              fingerprint_hash_type=None):
    '''
    Return the authorized keys for users

    CLI Example:

    .. code-block:: bash

        salt '*' ssh.auth_keys
        salt '*' ssh.auth_keys root
        salt '*' ssh.auth_keys user=root
        salt '*' ssh.auth_keys user="[user1, user2]"
    '''
    if not user:
        user = __salt__['user.list_users']()

    old_output_when_one_user = False
    if not isinstance(user, list):
        user = [user]
        old_output_when_one_user = True

    keys = {}
    for u in user:
        full = None
        try:
            full = _get_config_file(u, config)
        except CommandExecutionError:
            pass

        if full and os.path.isfile(full):
            keys[u] = _validate_keys(full, fingerprint_hash_type)

    if old_output_when_one_user:
        if user[0] in keys:
            return keys[user[0]]
        else:
            return {}

    return keys