import hashlib


def hash_crawl_arg(crawl_arg):
    """Take a crawl argument (ie. an identifying or authenticating factor)
    and create a hash. Hash will have the form <hash function name>:<hash digest>.
    """
    hash = hashlib.sha256(str(crawl_arg).encode('utf-8'))
    return '{hash_name}:{hash_digest}'.format(hash_name=hash.name, hash_digest=hash.hexdigest())