Remove v1/register's broken shared secret functionality

changelog.d/3703.removal

@@ -0,0 +1 @@
+The Shared-Secret registration method of the legacy v1/register REST endpoint has been removed. For a replacement, please see [the admin/register API documentation](https://github.com/matrix-org/synapse/blob/master/docs/admin_api/register_api.rst).

synapse/rest/client/v1_only/register.py

@@ -129,12 +129,9 @@ def on_POST(self, request):
             login_type = register_json["type"]
 
             is_application_server = login_type == LoginType.APPLICATION_SERVICE
-            is_using_shared_secret = login_type == LoginType.SHARED_SECRET
-
             can_register = (
                 self.enable_registration
                 or is_application_server
-                or is_using_shared_secret
             )
             if not can_register:
                 raise SynapseError(403, "Registration has been disabled")
@@ -144,7 +141,6 @@ def on_POST(self, request):
                 LoginType.PASSWORD: self._do_password,
                 LoginType.EMAIL_IDENTITY: self._do_email_identity,
                 LoginType.APPLICATION_SERVICE: self._do_app_service,
-                LoginType.SHARED_SECRET: self._do_shared_secret,
             }
 
             session_info = self._get_session_info(request, session)
@@ -325,56 +321,6 @@ def _do_app_service(self, request, register_json, session):
             "home_server": self.hs.hostname,
         })
 
-    @defer.inlineCallbacks
-    def _do_shared_secret(self, request, register_json, session):
-        assert_params_in_dict(register_json, ["mac", "user", "password"])
-
-        if not self.hs.config.registration_shared_secret:
-            raise SynapseError(400, "Shared secret registration is not enabled")
-
-        user = register_json["user"].encode("utf-8")
-        password = register_json["password"].encode("utf-8")
-        admin = register_json.get("admin", None)
-
-        # Its important to check as we use null bytes as HMAC field separators
-        if b"\x00" in user:
-            raise SynapseError(400, "Invalid user")
-        if b"\x00" in password:
-            raise SynapseError(400, "Invalid password")
-
-        # str() because otherwise hmac complains that 'unicode' does not
-        # have the buffer interface
-        got_mac = str(register_json["mac"])
-
-        want_mac = hmac.new(
-            key=self.hs.config.registration_shared_secret.encode(),
-            digestmod=sha1,
-        )
-        want_mac.update(user)
-        want_mac.update(b"\x00")
-        want_mac.update(password)
-        want_mac.update(b"\x00")
-        want_mac.update(b"admin" if admin else b"notadmin")
-        want_mac = want_mac.hexdigest()
-
-        if compare_digest(want_mac, got_mac):
-            handler = self.handlers.registration_handler
-            user_id, token = yield handler.register(
-                localpart=user.lower(),
-                password=password,
-                admin=bool(admin),
-            )
-            self._remove_session(session)
-            defer.returnValue({
-                "user_id": user_id,
-                "access_token": token,
-                "home_server": self.hs.hostname,
-            })
-        else:
-            raise SynapseError(
-                403, "HMAC incorrect",
-            )
-
 
 class CreateUserRestServlet(ClientV1RestServlet):
     """Handles user creation via a server-to-server interface