WiFiManager
WiFi Connection manager with web captive portal
...When your ESP starts up, it sets it up in Station mode and tries to connect to a previously saved Access Point. If this is unsuccessful (or no previous network saved) it moves the ESP into Access Point mode and spins up a DNS and WebServer (default ip 192.168.4.1). Using any wifi enabled device with a browser (computer, phone, tablet) connect to the newly created Access Point. Because of the Captive Portal and the DNS server you will either get a 'Join to network' type of popup or get any domain you try to access redirected to the configuration portal. ESP will try to connect. ...