Integrating Legacy JSESSIONID Authentication with Keycloak for Seamless Migration to Angular...

I’m working on migrating a legacy Java EE + GWT application to a modern Angular frontend using keycloak-angular for authentication. The legacy app uses traditional JSESSIONID-based authentication (form login with server-side session). We are gradually moving users to the new Angular app, and there's a key requirement from the client:

Users should not have to log in again when clicking a link from the legacy app to the new Angular app.

However, the legacy app must continue to use its current login mechanism, so we cannot fully replace it with Keycloak SSO (yet). What I need is a way to silently log in to Keycloak during or immediately after the legacy login process, so that when the user navigates to the new Angular app, they’re already authenticated there as well.

Context:

The new app uses keycloak-angular and expects the user to be authenticated using the Authorization Code Flow.

The legacy app does not interact with Keycloak at all.

Both apps run under the same root domain (e.g., example.com) but different ports or paths.

Continue reading...