Logout user via Keycloak REST API doesn't work

Finally, I've found the solution by looking at the Keycloak's source code: https://github.com/keycloak/keycloak/blob/9cbc335b68718443704854b1e758f8335b06c242/services/src/main/java/org/keycloak/protocol/oidc/endpoints/LogoutEndpoint.java#L169. It says:

If the client is a public client, then you must include a "client_id" form parameter.

So what I was missing is the client_id form parameter. My request should have been:

POST http://localhost:8080/auth/realms/<my_realm>/protocol/openid-connect/logout
Authorization: Bearer <access_token>
Content-Type: application/x-www-form-urlencoded

client_id=<my_client_id>&refresh_token=<refresh_token>

The session should be destroyed correctly.

Works with Keycloak 6.0.

Just for clarity: we do expire refreshToken, but accessToken IS STILL VALID while "Access Token Lifespan" time. Next time user tries to renew access token passing refresh token, Keycloak returns 400 Bad request, what should be catch and send as 401 Unauthorised response.

public void logout(String refreshToken) {
    try {
        MultiValueMap<String, String> requestParams = new LinkedMultiValueMap<>();
        requestParams.add("client_id", "my-client-id");
        requestParams.add("client_secret", "my-client-id-secret");
        requestParams.add("refresh_token", refreshToken);

        logoutUserSession(requestParams);

    } catch (Exception e) {
        log.info(e.getMessage(), e);
        throw e;
    }
}

private void logoutUserSession(MultiValueMap<String, String> requestParams) {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

    HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(requestParams, headers);

    String url = "/auth/realms/my-realm/protocol/openid-connect/logout";

    restTemplate.postForEntity(url, request, Object.class);
    // got response 204, no content
}

in version 3.4 you need as x-www-form-urlencoded body key client_id, client_secret and refresh_token.