Keycloak retrieve custom attributes to KeycloakPrincipal

In my rest service i can obtain the principal information after authentication using

KeycloakPrincipal kcPrincipal = (KeycloakPrincipal) servletRequest.getUserPrincipal();

statement.

Keycloak principal doesn't contain all the information i need about the authenticated user. Is it possible to customize my own principal type? On the keycloak-server-end I've developed a user federation provider. I saw that UserModel makes possible to add a set of custom attributes to my user.

Is it possible to insert my custom principal in that code?

Is it possible to retrieve this attributes from keycloak principal?

What is the way?

To add custom attributes you need to do three things:

1. Add attributes to admin console
2. Add claim mapping
3. Access claims

The first one is explained pretty good here: https://www.keycloak.org/docs/latest/server_admin/index.html#user-attributes

Add claim mapping:

1. Open the admin console of your realm.
2. Go to Clients and open your client
3. This only works for Settings > Access Type confidential or public (not bearer-only)
4. Go to Mappers
5. Create a mapping from your attribute to json
6. Check "Add to ID token"

Access claims:

final Principal userPrincipal = httpRequest.getUserPrincipal();

if (userPrincipal instanceof KeycloakPrincipal) {

    KeycloakPrincipal<KeycloakSecurityContext> kp = (KeycloakPrincipal<KeycloakSecurityContext>) userPrincipal;
    IDToken token = kp.getKeycloakSecurityContext().getIdToken();

    Map<String, Object> otherClaims = token.getOtherClaims();

    if (otherClaims.containsKey("YOUR_CLAIM_KEY")) {
        yourClaim = String.valueOf(otherClaims.get("YOUR_CLAIM_KEY"));
    }
} else {
    throw new RuntimeException(...);
}

I used this for a custom attribute I added with a custom theme.