Do not overwrite the cache with the decoded value of name_id, instead update a copy.

Author: Alexander Schrijver

src/saml2/cache.py

@@ -96,6 +96,7 @@ def get(self, name_id, entity_id, check_not_on_or_after=True):
         """
         cni = code(name_id)
         (timestamp, info) = self._db[cni][entity_id]
+        info = info.copy()
         if check_not_on_or_after and time_util.after(timestamp):
             raise ToOld("past %s" % str(timestamp))