<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def __get_yubico_users(username):
    '''
    Grab the YubiKey Client ID & Secret Key
    '''
    user = {}

    try:
        if __opts__['yubico_users'].get(username, None):
            (user['id'], user['key']) = list(__opts__['yubico_users'][username].values())
        else:
            return None
    except KeyError:
        return None

    return user