Remove mastodon posts on delete and OTP

backend/app/services/otp_service.py

@@ -0,0 +1,48 @@
+## Copyright © 2026 Olaf Kolkman
+## SPDX-License-Identifier: GPL-3.0-or-later
+
+import base64
+import hashlib
+import hmac
+import secrets
+import time
+from urllib.parse import quote
+
+
+def create_secret() -> str:
+    return base64.b32encode(secrets.token_bytes(20)).decode('ascii').rstrip('=')
+
+
+def provisioning_uri(secret: str, username: str, issuer: str = 'LinkLog') -> str:
+    return f'otpauth://totp/{quote(issuer)}:{quote(username)}?secret={secret}&issuer={quote(issuer)}'
+
+
+def current_code(secret: str, timestamp: float | None = None) -> str:
+    padded_secret = secret + '=' * (-len(secret) % 8)
+    key = base64.b32decode(padded_secret, casefold=True)
+    counter = int(timestamp if timestamp is not None else time.time()) // 30
+    digest = hmac.new(key, counter.to_bytes(8, 'big'), hashlib.sha1).digest()
+    index = digest[-1] & 0x0f
+    value = (int.from_bytes(digest[index:index + 4], 'big') & 0x7fffffff) % 1_000_000
+    return f'{value:06d}'
+
+
+def verify_code(secret: str | None, code: str | None) -> bool:
+    if not secret or not code:
+        return False
+    normalized_code = code.strip()
+    if len(normalized_code) != 6 or not normalized_code.isdigit():
+        return False
+    padded_secret = secret + '=' * (-len(secret) % 8)
+    try:
+        key = base64.b32decode(padded_secret, casefold=True)
+    except (ValueError, base64.binascii.Error):
+        return False
+    counter = int(time.time()) // 30
+    for offset in (-1, 0, 1):
+        digest = hmac.new(key, (counter + offset).to_bytes(8, 'big'), hashlib.sha1).digest()
+        index = digest[-1] & 0x0f
+        value = (int.from_bytes(digest[index:index + 4], 'big') & 0x7fffffff) % 1_000_000
+        if hmac.compare_digest(f'{value:06d}', normalized_code):
+            return True
+    return False