OIDC: add dynamic client registration util function (#3481)

* rename OidcDiscoveryError to OidcError

* oidc client registration functions

* test registerOidcClient

* tidy test file

* reexport OidcDiscoveryError for backwards compatibility

src/oidc/error.ts

@@ -0,0 +1,25 @@
+/*
+Copyright 2023 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.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+export enum OidcError {
+    NotSupported = "OIDC authentication not supported",
+    Misconfigured = "OIDC is misconfigured",
+    General = "Something went wrong with OIDC discovery",
+    OpSupport = "Configured OIDC OP does not support required functions",
+    DynamicRegistrationNotSupported = "Dynamic registration not supported",
+    DynamicRegistrationFailed = "Dynamic registration failed",
+    DynamicRegistrationInvalid = "Dynamic registration invalid response",
+}