feat(oauth): Add option to logout from OpenID Connect provider

* Fixes #598

Signed-off-by: Marvin A. Ruder <signed@mruder.dev>

backend/src/oauth/provider/discord.provider.ts

@@ -91,6 +91,7 @@ export class DiscordProvider implements OAuthProvider<DiscordToken> {
       providerId: user.id,
       providerUsername: user.global_name ?? user.username,
       email: user.email,
+      idToken: `discord:${token.idToken}`,
     };
   }