OAuth2 redirection issue with JHipster Gateway and Keycloak

Question

I've built an application using JHipster which consists of a gateway and a frontend with OAuth2 authentication implemented through Keycloak. Everything works as expected when running locally. However, when I deploy to a Kubernetes cluster, the redirection behavior differs, leading to authentication issues.

Local Setup:

When I authenticate locally, the flow is: frontend (/oauth2/authorization/oidc) -> gateway (on port 8080) -> Keycloak (for auth) -> gateway (with callback URL pointing to port 8080) -> frontend (port 9000 with session cookie). And everything works seamlessly.

Kubernetes Setup:

My frontend is behind an Nginx server with this configuration:

server {
    listen 80;

    location ~ ^/oauth2(.*)$ {
      return 302 https://gateway.test.internal/oauth2$1;
    }

    location / {
        root /usr/share/nginx/html;
        index index.html index.htm;
        try_files $uri $uri/ /index.html =404;
    }
}

When trying to authenticate, I'm redirected to the gateway at "https://gateway.test.internal/oauth2/authorization/oidc", then to Keycloak. After successful authentication in Keycloak, the callback URL points back to the gateway. However, instead of redirecting to the frontend at "https://web.test.internal/", I'm redirected to "https://gateway.test.internal/".

I tried adjusting the Nginx configuration:

server {
    listen 80;

    location /oauth2 {
      proxy_pass https://gateway.test.internal/oauth2;
    }

    location / {
        root /usr/share/nginx/html;
        index index.html index.htm;
        try_files $uri $uri/ /index.html =404;
    }
}

This resulted in an "invalid credentials" error from the gateway, which I suspect might be due to header issues (especially the "Referer" header).

To temporarily circumvent this, I added an endpoint in the gateway to manually handle the session cookie:

@GetMapping("/")
public ResponseEntity<Void> method(@CookieValue("SESSION") String session) {
    HttpCookie sessionCookie = ResponseCookie.from("SESSION", session).domain(".test.internal").build();

    return ResponseEntity
        .status(HttpStatus.FOUND)
        .location(URI.create("https://web.test.internal/"))
        .header(HttpHeaders.SET_COOKIE, sessionCookie.toString())
        .build();
}

However, with this, I have to manage the session cookies myself.

Has anyone experienced a similar problem or can they give me some pointers on how to correctly manage redirection when deploying the front end and the gateway with different sub-domains ?