Allow explicit configuration of OIDC dynamic registration metadata

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

docs/config.md

@@ -261,6 +261,46 @@ When Element is deployed alongside a homeserver with SSO-only login, some option
     ```
     It is most common to use the `immediate` flag instead of `on_welcome_page`.
 
+## Native OIDC
+
+Native OIDC support is currently in labs and is subject to change.
+
+Static OIDC Client IDs are preferred and can be specified under `oidc_static_clients` as a mapping from `issuer` to configuration object containing `client_id`.
+Issuer must have a trailing forward slash. As an example:
+
+```json
+{
+    "oidc_static_clients": {
+        "https://auth.example.com/": {
+            "client_id": "example-client-id"
+        }
+    }
+}
+```
+
+If a matching static client is not found, the app will attempt to dynamically register a client using metadata specified under `oidc_metadata`.
+The following subproperties are available:
+
+1. `client_uri`: This is the base URI for the OIDC client registration, typically `logo_uri`, `tos_uri`, and `policy_uri` must be either on the same domain or a subdomain of this URI.
+2. `logo_uri`: Optional URI for the client logo.
+3. `tos_uri`: Optional URI for the client's terms of service.
+4. `policy_uri`: Optional URI for the client's privacy policy.
+5. `contacts`: Optional list of contact emails for the client.
+
+As an example:
+
+```json
+{
+    "oidc_metadata": {
+        "client_uri": "https://example.com",
+        "logo_uri": "https://example.com/logo.png",
+        "tos_uri": "https://example.com/tos",
+        "policy_uri": "https://example.com/policy",
+        "contacts": ["support@example.com"]
+    }
+}
+```
+
 ## VoIP / Jitsi calls
 
 Currently, Element uses Jitsi to offer conference calls in rooms, with an experimental Element Call implementation in the works.

src/vector/platform/ElectronPlatform.tsx

@@ -446,13 +446,16 @@ export default class ElectronPlatform extends VectorBasePlatform {
         return (SdkConfig.get() as unknown as Record<string, string>)["web_base_url"] ?? "https://app.element.io";
     }
 
+    public get defaultOidcClientUri(): string {
+        // Default to element.io as our scheme `io.element.desktop` is within its scope on default MAS policies
+        return "https://element.io";
+    }
+
     public async getOidcClientMetadata(): Promise<OidcRegistrationClientMetadata> {
         const baseMetadata = await super.getOidcClientMetadata();
         return {
             ...baseMetadata,
             applicationType: "native",
-            // XXX: This should be overridable in config
-            clientUri: "https://element.io",
         };
     }