Get warned before an SSL certificate expires

from google.oauth2.credentials import Credentials
from googleapiclient.discovery import build
import base64, socket, ssl
from datetime import datetime, timezone
from email.mime.text import MIMEText
from clickruntime import on_trigger, credentials

SHEET_ID = "your-spreadsheet-id"

def days_left(host):
    with ssl.create_default_context().wrap_socket(socket.create_connection((host, 443), timeout=10), server_hostname=host) as s:
        exp = datetime.strptime(s.getpeercert()["notAfter"], "%b %d %H:%M:%S %Y %Z").replace(tzinfo=timezone.utc)
    return (exp - datetime.now(timezone.utc)).days

@on_trigger
def run(event):
    creds = Credentials(credentials.connection("google", "work"))
    sheets = build("sheets", "v4", credentials=creds, cache_discovery=False).spreadsheets()
    hosts = [r[0] for r in sheets.values().get(spreadsheetId=SHEET_ID, range="Domains!A2:A").execute().get("values", []) if r]
    out, soon = [], []
    for h in hosts:
        try:
            d = days_left(h)
        except Exception:
            d = "unreachable"
        out.append([d])
        if d == "unreachable" or d < 14:
            soon.append(f"{h}: {d}")
    sheets.values().update(spreadsheetId=SHEET_ID, range="Domains!B2", valueInputOption="RAW", body={"values": out}).execute()
    if soon:
        msg = MIMEText("\n".join(soon))
        msg["to"], msg["subject"] = "you@example.com", f"{len(soon)} SSL certificate(s) need attention"
        build("gmail", "v1", credentials=creds, cache_discovery=False).users().messages().send(
            userId="me", body={"raw": base64.urlsafe_b64encode(msg.as_bytes()).decode()}).execute()
    return {"checked": len(hosts), "alerts": len(soon)}