How to get access_token within keycloak customized required_action to call keycloak's own client service

We are working on a required action in KeyCloak, that needs to send data to another service(A) via POST. This service is also integrated with KeyCloak, so we have to provide an Authorization header with the user’s token. From the required action, we have the user’s details (email, etc.), but we’re trying to get the Auth token for that user in order to use it to call service-A. Question: how does one get the user’s auth token from the required action in Java code?
public class CutomizedRequiredAction
implements RequiredActionProvider, RequiredActionFactory, DisplayTypeRequiredActionFactory {
public void processAction(RequiredActionContext context) {
AuthenticationSessionModel authSession = context.getAuthenticationSession();
RealmModel realm = context.getRealm();
UserModel user = context.getUser();
KeycloakSession session = context.getSession();

// we need the user’s auth token here to call our Service-A’s POST endpoint