1 files changed, 14 insertions, 0 deletions
diff --git a/synapse/util/stringutils.py b/synapse/util/stringutils.py
index 69dffd8244..5fb18ee1f8 100644
--- a/synapse/util/stringutils.py
+++ b/synapse/util/stringutils.py
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2020 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -14,12 +15,15 @@
 # limitations under the License.
 
 import random
+import re
 import string
 
 import six
 from six import PY2, PY3
 from six.moves import range
 
+from synapse.api.errors import Codes, SynapseError
+
 _string_with_symbols = (
     string.digits + string.ascii_letters + ".,;:^&*-_+=#~@"
 )
@@ -29,6 +33,8 @@ _string_with_symbols = (
 # we get cryptographically-secure randoms.
 rand = random.SystemRandom()
 
+client_secret_regex = re.compile(r"^[0-9a-zA-Z.=_-]+$")
+
 
 def random_string(length):
     return ''.join(rand.choice(string.ascii_letters) for _ in range(length))
@@ -113,3 +119,11 @@ def exception_to_unicode(e):
         return msg.decode('utf-8', errors='replace')
     else:
         return msg
+
+
+def assert_valid_client_secret(client_secret):
+    """Validate that a given string matches the client_secret regex defined by the spec"""
+    if client_secret_regex.match(client_secret) is None:
+        raise SynapseError(
+            400, "Invalid client_secret parameter", errcode=Codes.INVALID_PARAM
+        )