...
#include <PubSubClient.h>
#include "password.h"

const char* ssid = WIFI_SSID;
const char* password = WIFI_PASSWORD;

const char* mqtt_server = MQTT_SERVER;
int mqtt_server_port = 18772;
const char* mqtt_username = MQTT_USENAME;
const char* mqtt_password = MQTT_PASSWORD;


====================================================
password.h

#define WIFI_SSID "ssid"
#define WIFI_PASSWORD "password"
#define MQTT_SERVER "server"
....