Breaking changes
* The return type of `get_id_email` is now `Tuple[str, Optional[str])`, which means the email is now optional and **can be `None`**.
* This will help to better support providers that don't always provide an email address.
New features and improvements
* New OpenID client, with automatic endpoints discovery. [[Documentation](https://frankie567.github.io/httpx-oauth/oauth2/#openid)]
* Okta client implementation revamped using the OpenID client as a basis.