* Retrieve the token provider
* @return the token provider or {@code null}.
*/
@CheckForNull
private TokenProvider getTokenProvider() {
TokenProvider provider = null;
SecurityProvider securityProvider = getSecurityProvider();
Root root = getRoot();
if (root != null && securityProvider != null) {
TokenConfiguration tokenConfig = securityProvider.getConfiguration(TokenConfiguration.class);
provider = tokenConfig.getTokenProvider(root);