I have created a PreSignup Lambda function to be used with Cognito Pre-SignUp trigger with the following code:

import { APIGatewayEventDefaultAuthorizerContext, APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda';

export async function PreSignup(event: any, context: APIGatewayEventDefaultAuthorizerContext,) {
  console.log("...event:", event);
  console.log("...context:", context);

  let userName = event.userName;
  let email = event.request.userAttributes.email;

  console.log("...userName:", userName);
  console.log("...email:", email);

  // Confirming the event so Cogntio doesnt resend it again:
  event.response.autoConfirmUser = true;
  event.response.autoVerifyPhone = true;
  event.response.autoVerifyEmail = true;
  return event;
}

Instead of setting up the event to any with function PreSignup(event: any) I would rather specify a type of the event.

I tried to specify it as APIGatewayProxyEvent like so:

function PreSignup(event: APIGatewayProxyEvent, context: APIGatewayEventDefaultAuthorizerContext,) {...}

but it doesn't work as the event sent by Cognito Pre Sign-Up trigger is not a APIGatewayProxyEvent type. What kind of event is it?

Edited later:

Below is copy/pasted event that was pushed by Cognito PreSignUp Trigger:

{
  version: '1',
  region: 'us-east-1',
  userPoolId: 'us-east-1_abcdef',
  userName: 'emailf@address.com',
  callerContext: {
    awsSdkVersion: 'aws-sdk-nodejs-2.799.0',
    clientId: 'CLIENT_ID_NOT_APPLICABLE'
  },
  triggerSource: 'PreSignUp_AdminCreateUser',
  request: {
    userAttributes: { email: 'emailf@address.com' },
    validationData: null
  },
  response: {
    autoConfirmUser: false,
    autoVerifyEmail: false,
    autoVerifyPhone: false
  }
}

Below is an example of another AWS event this time pushed by AWS EventBridge (similar to the one pushed by Cognito Trigger):

{
  version: '0',
  id: '0ee136cb-ea53-f9e0-a6a9-232dfb78b7d0',
  'detail-type': 'UserCreated',
  source: 'my.company.endpointname',
  account: '123456789012',
  time: '2021-01-29T03:05:54Z',
  region: 'us-east-1',
  resources: [],
  detail: { foo: 'bar', createdAt: 1611889553709 }
}