Add SameSite support

gluon/globals.py

@@ -1075,6 +1075,8 @@ class Session(Storage):
             scookies['HttpOnly'] = True
         if self._secure:
             scookies['secure'] = True
+        if self._same_site:
+            scookies['samesite'] = self._same_site
 
     def clear_session_cookies(self):
         request = current.request
@@ -1153,6 +1155,12 @@ class Session(Storage):
     def secure(self):
         self._secure = True
 
+    def samesite(self, mode='Lax'):
+        if 'samesite' not in Cookie.Morsel._reserved:
+            # Python version 3.7 and lower needs this
+            Cookie.Morsel._reserved['samesite'] = 'SameSite'
+        self._same_site = mode
+
     def forget(self, response=None):
         self._close(response)
         self._forget = True
@@ -1180,7 +1188,7 @@ class Session(Storage):
 
     def _unchanged(self, response):
         if response.session_new:
-            internal = ['_last_timestamp', '_secure', '_start_timestamp']
+            internal = ['_last_timestamp', '_secure', '_start_timestamp', '_same_site']
             for item in self.keys():
                 if item not in internal:
                     return False