enforce integer for max-age cookie

sanic/cookies.py

@@ -1,6 +1,7 @@
 import re
 import string
 
+DEFAULT_MAX_AGE = 0
 
 # ------------------------------------------------------------ #
 #  SimpleCookie
@@ -103,6 +104,9 @@ class Cookie(dict):
         if key not in self._keys:
             raise KeyError("Unknown cookie property")
         if value is not False:
+            if key.lower() == "max-age":
+                if not str(value).isdigit():
+                    value = DEFAULT_MAX_AGE
             return super().__setitem__(key, value)
 
     def encode(self, encoding):