PostAuthentication - auto verify phone_number (not in PreSignUp)

Hello All, Cognito/Amplify Team,

I am implementing passwordless SMS auth. Flow is: signIn -> error (userNotFound) -> signUp -> signIn -> OTP sent to mobile -> OTP entered by user -> confirmSignIn -> success and user is logged in. This flow works and user is able to successfully sign in. But verification of phone_number should better happen in PostAuthentication (after user is signed in after entering and successfully checking OTP) and not before that in PreSignUp.

I have following lambdas: PreSignUp, DefineAuthChallenge, CreateAuthChallenge, VerifyAuthChallengeResponse, PostAuthentication. Things have run fine. Want to change one thing for good: Auto verify phone number in Post Authentication instead of PreSignUp lambda. How to do that? I thought following can do it in PostAuthentication lambda:

    event.response.phone_number_verified = "true"

it did not. I also tried with setting:

event.request.userAttributes.phone_number_verified = "true"

it also did not. In PreSignUp, following did work fine:

event.response.autoVerifyPhone = true;

PostAuthentication lambda (custom.js):

exports.handler = async (event, context) => {
  console.log('Received EVENT', JSON.stringify(event, null, 2));                      if (event.request.userAttributes.hasOwnProperty("email")                                 && event.request.userAttributes.email_verified != "true") {                   
      event.request.userAttributes.email_verified = "true"                            
      event.response.email_verified = "true";
  }   
  if (event.request.userAttributes.hasOwnProperty("phone_number")              && event.request.userAttributes.phone_number_verified != "true") {   
      event.request.userAttributes.phone_number_verified = "true";  
      event.response.phone_number_verified = "true";   
  } 
  console.log('Returning event', JSON.stringify(event, null, 2))                      
  return event;                                                                       
};

PreSignUp (custom.js):

"use strict";
exports.handler = async (event) => {
    console.log('Received EVENT', JSON.stringify(event, null, 2));
    event.response.autoConfirmUser = true;
    /*
    if (event.request.userAttributes.hasOwnProperty("email")) {
        event.response.autoVerifyEmail = true;
    }
    if (event.request.userAttributes.hasOwnProperty("phone_number")) {
        event.response.autoVerifyPhone = true;
    }
    */
    console.log('Returning EVENT', JSON.stringify(event, null, 2));
    return event;

But when I check user in Cognito, it still shows as NotVerified. [1] which is in TS but also suggest to set: event.request.userAttributes.email_verified = "true"
[2] does not suggest how to auto verify phone_number in PostAuthentication lambda. [3] does suggest how to auto verify phone_number in PreSignUp.

[1] https://github.com/aws-samples/amazon-cognito-passwordless-email-auth/blob/master/cognito/lambda-triggers/post-authentication/post-authentication.ts [2] https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-post-authentication.html [3] https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-pre-sign-up.html

Can you help resolve this. How/what to set in PostAuthentication to auto verification of phone number?

Thanks in advance.