Error 403 accessing admin/groups OIDC API from Keycloak

Thomas Escolan :

Using keycloak-authz-client (6.0.1) only (no Spring Security), I need to read user informations AND user groups from my service provider.

After getting a proper access token, thanks to the AuthzClient, I was able to reach user information API:

    UriBuilder target = UriBuilder.fromUri(kcURL);
    target.path("realms/{realm}/protocol/openid-connect/userinfo")
          .resolveTemplate("realm", this.realm);

    UserInfoOIDC info = new UserInfoOIDC();
    try {
        UserInfo response = this.buildBearerInvocation(target, accessToken).get(UserInfo.class);
        info.setName(response.getName());
        info.setUsername(response.getPreferredUsername());
        info.setCompleted(true);
        log.info("User info successfully retrieved from {}", this.realm);
    } catch (WebApplicationException e) {
        log.error("User info failure on {}: {}", this.realm, e.getMessage());
    }
...
    private Invocation.Builder buildBearerInvocation(UriBuilder target, String accessToken) {
        WebTarget webTarget = restClient.target(target);
        Invocation.Builder builder = webTarget.request(APPLICATION_JSON)
                .header(AUTHORIZATION, "Bearer " + accessToken);
        return builder;
    }

But I couldn't access the "admin API":

    UriBuilder target = UriBuilder.fromUri(kcURL);
    target.path("admin/realms/" + this.realm);
    target.path("users/" + userId);
    target.path("groups");
    try {
        return this.buildBearerInvocation(target, accessToken)
                .get(GroupRepresentation.class);
    } catch (WebApplicationException e) {
        log.error("User groups failure on realms {}: {}", this.realm, e.getMessage());
    }

[main] INFO com.LoggingFilter - Processing http://localhost:8080/auth/admin/realms/TestRealm/users/0f443554-01d0-4b40-a652-0c8c174632d4/groups [main] ERROR com.KeycloakProvider - User groups failure on realms TestRealm: HTTP 403 Forbidden

I'm wondering if that might simply come from insufficient user access rights or rather from a CORS issue here (I've added "127.0.0.1 localhost-auth" to my etc/hosts file, not sure at all that would be of any help here, though). How can I open the "admin API" to a user, more CORS configuration or any special role for the user?

EDITED - the Keycloak Admin Client won't help here (HTTP 403 Forbidden as well):

    @Test
    public void checkKeycloakAdminClient() {
        Keycloak client = KeycloakBuilder.builder()
                .serverUrl(url)
                .realm(realm)
                .username(adminUsername)
                .password(adminPassword)
                .clientId(clientId)
                .clientSecret(clientSecret)
                .build();
        RealmResource realmResource = client.realm(realm);

        UsersResource usersResource = realmResource.users();
        List<UserRepresentation> users = usersResource.search(username);
    }

Thomas Escolan :

Assign all "view-..." and "query-..." available Client Roles from "realm-management" realm's client to the admin user (see User/Role Mappings).