Custom Authenticator Field Validation

### On which framework/platform would you like to see this feature implemented?

React, Angular, Vue, React Native

### Which UI component is this feature-request for?

Authenticator

### Please describe your feature-request in detail.

I would like to be able to add custom event validation for specific fields in the `Authenticator`, for example being able to run validation blur events for custom username requirements

### Please describe a solution you'd like.

_No response_

### We love contributors! Is this something you'd be interested in working on?

- [X] 👋 I may be able to implement this feature request.
- [ ] ⚠️ This feature might incur a breaking change.

Start by reviewing the Authenticator component across the React, Angular, Vue, and React Native platforms to determine how field events and validation are currently exposed. Define the custom validation behavior and supported event API before identifying the relevant tests; done means custom username or other field validation can run on blur without breaking existing Authenticator behavior.

Written by the indexing model from the issue text.