Update configuration and access control for Telegram miniapp

- Added ALLOWED_USERNAMES and ADMIN_USERNAMES to .env.example for user access control.
- Implemented validation of Telegram Web App initData in a new telegram_auth.py module.
- Enhanced API to check user access before fetching duties.
- Updated README with instructions for configuring miniapp access.
- Modified .dockerignore and .gitignore to include data directory and database files.

api/telegram_auth.py

@@ -0,0 +1,61 @@
+"""Validate Telegram Web App initData and extract user username."""
+import hashlib
+import hmac
+import json
+from urllib.parse import unquote
+
+# Telegram algorithm: https://core.telegram.org/bots/webapps#validating-data-received-via-the-mini-app
+# Data-check string must use the same key=value pairs as received (sorted by key); we preserve raw values.
+
+
+def validate_init_data(init_data: str, bot_token: str) -> str | None:
+    """
+    Validate initData signature and return the Telegram username (lowercase, no @).
+    Returns None if data is invalid, forged, or user has no username.
+    """
+    if not init_data or not bot_token:
+        return None
+    init_data = init_data.strip()
+    # Parse preserving raw values for HMAC (key -> raw value)
+    params = {}
+    for part in init_data.split("&"):
+        if "=" not in part:
+            continue
+        key, _, value = part.partition("=")
+        if not key:
+            continue
+        params[key] = value
+    hash_val = params.pop("hash", None)
+    if not hash_val:
+        return None
+    # Build data-check string: keys sorted, format key=value per line (raw values)
+    data_pairs = sorted(params.items())
+    data_string = "\n".join(f"{k}={v}" for k, v in data_pairs)
+    # secret_key = HMAC-SHA256(key=b"WebAppData", msg=bot_token.encode()).digest()
+    secret_key = hmac.new(
+        b"WebAppData",
+        msg=bot_token.encode(),
+        digestmod=hashlib.sha256,
+    ).digest()
+    # computed = HMAC-SHA256(key=secret_key, msg=data_string.encode()).hexdigest()
+    computed = hmac.new(
+        secret_key,
+        msg=data_string.encode(),
+        digestmod=hashlib.sha256,
+    ).hexdigest()
+    if not hmac.compare_digest(computed.lower(), hash_val.lower()):
+        return None
+    # Parse user JSON (value may be URL-encoded in the raw string)
+    user_raw = params.get("user")
+    if not user_raw:
+        return None
+    try:
+        user = json.loads(unquote(user_raw))
+    except (json.JSONDecodeError, TypeError):
+        return None
+    if not isinstance(user, dict):
+        return None
+    username = user.get("username")
+    if not username or not isinstance(username, str):
+        return None
+    return username.strip().lstrip("@").lower()