from typing import Dict
from typing import Any
from typing import cast


def handle_url_verification(item: Dict[str, Any]) -> str:
    """
    Handles a Slack url_verification request:
    https://api.slack.com/events/url_verification
    """
    challenge = item.get("challenge")
    if challenge is None:
        raise ValueError("No challenge in Slack URL verification request")
    cast(str, challenge)
    return challenge