<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_auth(username, password):
    '''
    Returns the HTTP auth header
    '''
    if username and password:
        return requests.auth.HTTPBasicAuth(username, password)
    else:
        return None