Fix V2 catalog and tag pagination

util/pagination.py

@@ -0,0 +1,26 @@
+import datetime
+import json
+
+from app import app
+from util.security.crypto import encrypt_string, decrypt_string
+
+# TTL (in seconds) for page tokens.
+_PAGE_TOKEN_TTL = datetime.timedelta(days=2).total_seconds()
+
+def decrypt_page_token(token_string):
+  if token_string is None:
+    return None
+
+  unencrypted = decrypt_string(token_string, app.config['PAGE_TOKEN_KEY'], ttl=_PAGE_TOKEN_TTL)
+  if unencrypted is None:
+    return None
+
+  try:
+    return json.loads(unencrypted)
+  except ValueError:
+    return None
+
+
+def encrypt_page_token(page_token):
+  return encrypt_string(json.dumps(page_token), app.config['PAGE_TOKEN_KEY'])
+