WiFiManager/examples/OnDemandConfigPortal/OnDemandConfigPortal.ino

#include <ESP8266WiFi.h>          //https://github.com/esp8266/Arduino

//needed for library
#include <DNSServer.h>
#include <ESP8266WebServer.h>
#include <WiFiManager.h>          //https://github.com/tzapu/WiFiManager


//callback notifying us of the need to save config
void saveConfigCallback () {
  Serial.println("Should save config");
}


void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.println("\n Starting");

  //read gpio 4 state on startup
  pinMode(4, INPUT);
  int pinState = digitalRead(4);

  //if gpio 4 is high startup config mode
  if (pinState == HIGH) {
    //WiFiManager
    //Local intialization. Once its business is done, there is no need to keep it around
    WiFiManager wifiManager;

    //set config save notify callback
    wifiManager.setSaveConfigCallback(saveConfigCallback);

    //reset settings - for testing
    //wifiManager.resetSettings();

    //sets timeout until configuration portal gets turned off
    //useful to make it all retry or go to sleep
    //in seconds
    //wifiManager.setTimeout(120);

    //it starts an access point with the specified name
    //here  "AutoConnectAP"
    //and goes into a blocking loop awaiting configuration

    //WITHOUT THIS THE AP DOES NOT SEEM TO WORK PROPERLY WITH SDK 1.5 , update to at least 1.5.1
    //WiFi.mode(WIFI_STA);
    
    if (!wifiManager.startConfigPortal("OnDemandAP")) {
      Serial.println("failed to connect and hit timeout");
      delay(3000);
      //reset and try again, or maybe put it to deep sleep
      ESP.reset();
      delay(5000);
    }

    //if you get here you have connected to the WiFi
    Serial.println("connected...yeey :)");
  }


}

void loop() {
  // put your main code here, to run repeatedly:


}