User Profile Form at Sign-up

## Problem

Currently the user profile can only be captured after the user is signed up, and the developer need to implement the form by themselves in their application

This will leads to
- users being created without the necessary fields
- extra effort in building the form which should be included in the signup process

## Appetite

6 weeks

## Solution

### Overview

Collect standard/custom attributes in AuthUI during the signup flow. Some can be specified to be Mandatory so that it must be provided in order to complete signup.

### Configuration
In the portal, under "**User Profile**", add a page called "Signup Profile"
- User can define which attributes should be captured in the sign up form
- The order of presentation can be changed.
- User can customize the label that being displayed in the form, they can be different from the attribute name.
- Attributes can be set mandatory
- Validation can be set for each field, it's already possible in attribute settings page.
- Further custom validation can be done by event hook

### Sign up flow

- After setting the identity and authenticator, the profile form will be shown.
- The end user must complete all mandatory fields to complete the sign up

## Rabbit Holes

//

## No Goes

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Start with the portal's User Profile > Signup Profile entry point and trace the signup flow after identity and authenticator setup. Define the configuration and flow boundaries before implementation; done means configurable ordered, labeled, validated standard or custom attributes, mandatory-field enforcement, and event-hook validation during signup.

Written by the indexing model from the issue text.