Can we share WiFi SSID and Password through WAC, I found a arduino library which support for apple HomeKit and I successfully integrated a Light Bulb but the disadvantage is the WiFi SSID and Password should be hard coded before it flash to the ESP. I tried WiFiManager to avoid this problem but as per my understanding it also not a permanent solution.
So can we use WAC in apple in order to share WiFi credentials with ESP?
WAC uses BLE (Bluetooth Low Energy) to communicate with the device. The ESP8266 doesn't support Bluetooth. So there's absolutely no chance of doing this without adding extra hardware to use BLE.
WAC is also only available for devices which have been certified through Apple's MFi program. MFi used to require that the device use a custom Apple security chip; not sure if it still does. Part of MFi certification is extensive testing of the device.
So even if you add BLE support you're not going to just casually support WAC.