I know firebase sdk have a built in function to verified recaptcha response before doing sign-in with phone number but, it is possible using manual captcha verifier API return response from https://www.google.com/recaptcha/api/siteverify as 2nd parameter in firebase.auth().signInWithPhoneNumber(phone, apiResponse) ?
I have different case to do it manually.
Thanks
With Recaptcha, you can introduce your own authorization method by using a decodable JWT as a second input. this will require a source of validation to generate the correct token
const captchaVerifier = {
type: 'recaptcha',
verify: () => Promise.resolve(token)
};
Source: https://pastebin.com/kaCarKC5
You could also make your own ReCaptcha that triggers the invisible ReCaptcha or simply use invisible ReCaptcha and implement your own later on per your app's design.
Reference: Invisible ReCaptcha