A realm that does not exist in Keycloak causes an IllegalArgumentException exception

[rusiaikinat]

Environment

Version: 2026.1.999-SNAPSHOT

Bug Description

When testing a BPM engine connection with authentication type OAuth 2 (Client/Secret), if the realm specified in Issuer URI does not exist (or is unreachable for OIDC discovery), the application shows the user the raw text of an unhandled IllegalArgumentException instead of the standard localized error notification (oauth2AutorizationFailure.*).

Steps To Reproduce

1. Administration → BPM engines → Create (or edit an existing engine).
2. Authentication → Enabled → Type = OAuth 2 (Client/Secret).
3. Set Issuer URI to a nonexistent realm, e.g. http://localhost:8180/realms/sample3 (realm sample3 does not exist in Keycloak).
4. Fill in any values for Client ID / Client secret.
5. Click Test connection.

Current Behavior

IllegalArgumentException: Unable to resolve Configuration with the provided Issuer of "http://localhost:8180/realms/sample3", errors: [404 Not Found on GET request for "http://localhost:8180/realms/sample3/.well-known/openid-configuration": "{"error":"Realm does not exist"}", 404 Not Found on GET request for "http://localhost:8180/.well-known/openid-configuration/realms/sample3": "{"error":"HTTP 404 Not Found"}", 404 Not Found on GET request for "http://localhost:8180/.well-known/oauth-authorization-server/realms/sample3": "{"error":"Realm does not exist"}"]