I have an Apple Developer Account. I'm trying use "sign in with apple" option. But that endpoint required "client ID" and "client secret" fields. I can't find my clientID and clientSecret on my Apple developer page.
Client ID is your App ID(IDENTIFIER) refer link https://developer.apple.com/account/resources/identifiers/list
Client Secret is JWT you need to create As per Apple's doc Client_Secret: A secret JSON Web Token, generated by the developer, that uses the Sign in with Apple private key associated with your developer account. Authorization code and refresh token validation requests require this parameter. Link:- https://developer.apple.com/documentation/sign_in_with_apple/generate_and_validate_tokens
I'm not sure while language you are using but if you can work with Javascript then below link which is well documented with example will help in getting Client_secret.
https://github.com/jooyoungho/apple-token-revoke-in-firebase