First Logon
The default password for both the AP and for web login upon initial login is password1234
https://github.com/jjssoftware/iD8266/blob/master/iD8266/flashAppData.h#L21
Once the firmware is flashed and the device is first time booted, it will automatically be in access point mode. The AP IP address is the default 192.168.4.1. Connect to this AP using the default AP password1234 password.
Once you've connected to the AP, you should be able to see the login page if you navigate to http://192.168.4.1 in a browser.
When you login for the first time you will be prompted to change the default password and when you do this, it will change the password for both the AP and also the admin web logon account to your new password.