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

def _format_auth_line(key, enc, comment, options):
    '''
    Properly format user input.
    '''
    line = ''
    if options:
        line += '{0} '.format(','.join(options))
    line += '{0} {1} {2}\n'.format(enc, key, comment)
    return line