getting #error=login_required when trying to use onLoad: 'check-sso'

[Faedryth]

Bug Report or Feature Request (mark with an x)

- [X] bug report -> please search for issues before submitting
- [ ] feature request

Versions.

angular 16.2.0
keycloak-angular: 14.2.0
keycloak-js: 25.0.0

Repro steps.

I have an application that has been working well with onLoad: 'login-required' for some time, using Microsoft as IDP.
Now I'm trying to use SSO to avoid the redirection to Microsoft and reloading the SPA everytime I start the app, but I'm always getting an #error=login_required error.

This is how I intitialize keycloak: I'm trying the SSO method, then I force to login() if the user is not logged in after the SSO check:

        keycloak
            .init({
                config: {
                    url: environment.keycloak.url,
                    realm: environment.keycloak.realm,
                    clientId: environment.keycloak.clientIdIntra
                },
                loadUserProfileAtStartUp: true,
                initOptions: {
                    onLoad: 'check-sso',
                    silentCheckSsoRedirectUri: window.location.origin + '/assets/silent-check-sso.html'
                }
            })
            .then(() => {
                return keycloak.isLoggedIn();
            })
            .then((isLoggedIn) => {
                if (!isLoggedIn) keycloak.login({ redirectUri: window.location.href });

And I created the silent-check-sso.html page under my asset folder as indicated in your setup guide.

But I'm always redirected to the login page, meaning the SSO never catches the previous session. And if I look in the network tab, I can see this "/auth" call: https://MyKeycloakServer/realms/MyRealm/protocol/openid-connect/auth?client_id=MyClientId...

Which always has this in its response's headers, note the "#error=login_required" part:
http://localhost:4200/intra/assets/silent-check-sso.html#error=login_required&state=XXXX&iss=MyRealm

Desired functionality.

I'd like the silent SSO check to retrieve the previous session if it's still active
Am I doing something wrong?