GOG Login: Nahtloser Auth-Flow wie Steam (kein Code-Paste noetig)

- Electron: Fängt GOG Redirect automatisch ab (will-redirect Interceptor)
- Code-Exchange passiert im Hintergrund, User sieht nur Erfolgs-Popup
- GOG Auth-URLs (auth.gog.com, login.gog.com, embed.gog.com) in Popup erlaubt
- Server: GET /gog/login Redirect + POST /gog/exchange Endpoint
- Browser-Fallback: Code-Paste Dialog falls nicht in Electron
- gog.ts: Feste redirect_uri (embed.gog.com/on_login_success)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/plugins/game-library/gog.ts

@@ -10,6 +10,7 @@ const GOG_CLIENT_SECRET =
 const GOG_AUTH_URL = 'https://auth.gog.com/auth';
 const GOG_TOKEN_URL = 'https://auth.gog.com/token';
 const GOG_EMBED_URL = 'https://embed.gog.com';
+const GOG_REDIRECT_URI = 'https://embed.gog.com/on_login_success?origin=client';
 
 // ── Types ────────────────────────────────────────────────────────────────────
 
@@ -37,13 +38,13 @@ export interface GogGame {
 
 /**
  * Build the GOG OAuth authorization URL that the user should visit to grant
- * access.  After approval, GOG will redirect to `redirectUri` with a `code`
- * query parameter.
+ * access.  After approval, GOG redirects to `embed.gog.com/on_login_success`
+ * with a `code` query parameter that the user copies back into the app.
  */
-export function getGogAuthUrl(redirectUri: string): string {
+export function getGogAuthUrl(): string {
   const params = new URLSearchParams({
     client_id: GOG_CLIENT_ID,
-    redirect_uri: redirectUri,
+    redirect_uri: GOG_REDIRECT_URI,
     response_type: 'code',
     layout: 'client2',
   });
@@ -53,10 +54,10 @@ export function getGogAuthUrl(redirectUri: string): string {
 
 /**
  * Exchange an authorization code for GOG access + refresh tokens.
+ * Uses the fixed GOG_REDIRECT_URI that matches the OAuth registration.
  */
 export async function exchangeGogCode(
   code: string,
-  redirectUri: string,
 ): Promise<GogTokens> {
   console.log('[GOG] Exchanging authorization code for tokens...');
 
@@ -65,7 +66,7 @@ export async function exchangeGogCode(
     client_secret: GOG_CLIENT_SECRET,
     grant_type: 'authorization_code',
     code,
-    redirect_uri: redirectUri,
+    redirect_uri: GOG_REDIRECT_URI,
   });
 
   const res = await fetch(`${GOG_TOKEN_URL}?${params.toString()}`);