### Question:
PlainServerCallbackHandler implements AuthenticateCallbackHandler { boolean authenticate(String username, char[] pass) throws IOException { if (username == null) { return false; } else { boolean ret = false; log.info("GET OPERATION " + username + ":" + new String(pass)); String sessionKey = ""; if (username.equals("admin")) { String expectedPass = "admin-secret"; ret = expectedPass.equals(new String(pass)); } else if (username.equals(ZOOKEPER)) { String expectedPass = ZOOKEPER; ret = expectedPass.equals(new String(pass)); } else if (username.equals(SCHEMA_REGISTRY)) { String expectedPass = SCHEMA_REGISTRY; ret = expectedPass.equals(new String(pass)); } else { try { sessionKey = join(username, new String(pass)); if (sessionKey != null && !"".equals(sessionKey)) { ret = true; } } catch (Exception e) { log.warning(e.getMessage()); } } log.info("RETURN GET OPERATION " + username + ":" + new String(pass) + " RET " + ret); return ret; } }  @Override void configure(Map<String, ?> configs, String mechanism, List<AppConfigurationEntry> jaasConfigEntries); @Override void handle(Callback[] callbacks); @Override void close();  }### Answer:
@Test public void getUserToken() throws Exception { String token = ""; String deviceId = ""; boolean authenticate = plainServerCallbackHandler.authenticate(deviceId, token.toCharArray()); assertTrue(authenticate); }