Allow . and ~ chars in registration tokens (#10887)

Per updates to MSC3231 in order to use the same grammar
as other identifiers.

changelog.d/10887.bugfix

@@ -0,0 +1 @@
+Allow the `.` and `~` characters when creating registration tokens as per the change to [MSC3231](https://github.com/matrix-org/matrix-doc/pull/3231).

synapse/rest/admin/registration_tokens.py

@@ -113,7 +113,7 @@ class NewRegistrationTokenRestServlet(RestServlet):
         self.store = hs.get_datastore()
         self.clock = hs.get_clock()
         # A string of all the characters allowed to be in a registration_token
-        self.allowed_chars = string.ascii_letters + string.digits + "-_"
+        self.allowed_chars = string.ascii_letters + string.digits + "._~-"
         self.allowed_chars_set = set(self.allowed_chars)
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:

tests/rest/admin/test_registration_tokens.py

@@ -95,8 +95,10 @@ class ManageRegistrationTokensTestCase(unittest.HomeserverTestCase):
 
     def test_create_specifying_fields(self):
         """Create a token specifying the value of all fields."""
+        # As many of the allowed characters as possible with length <= 64
+        token = "adefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789._~-"
         data = {
-            "token": "abcd",
+            "token": token,
             "uses_allowed": 1,
             "expiry_time": self.clock.time_msec() + 1000000,
         }
@@ -109,7 +111,7 @@ class ManageRegistrationTokensTestCase(unittest.HomeserverTestCase):
         )
 
         self.assertEqual(200, int(channel.result["code"]), msg=channel.result["body"])
-        self.assertEqual(channel.json_body["token"], "abcd")
+        self.assertEqual(channel.json_body["token"], token)
         self.assertEqual(channel.json_body["uses_allowed"], 1)
         self.assertEqual(channel.json_body["expiry_time"], data["expiry_time"])
         self.assertEqual(channel.json_body["pending"], 0)
@@ -193,7 +195,7 @@ class ManageRegistrationTokensTestCase(unittest.HomeserverTestCase):
         """Check right error is raised when server can't generate unique token."""
         # Create all possible single character tokens
         tokens = []
-        for c in string.ascii_letters + string.digits + "-_":
+        for c in string.ascii_letters + string.digits + "._~-":
             tokens.append(
                 {
                     "token": c,