[keycloak-dev] Profile SPI

At the moment there is no single point to define validation for a user. Even worse for the account management console and admin console it's not even possible to define validation for custom attributes. Also, as there is no defined list of attributes for a user there the mapping of user attributes is error prone. I'd like to introduce a Profile SPI to help with this. It would have methods to: * Validate users during creation and updates * List defined attributes on a user There would be a built-in provider that would delegate to ProfileAttribute SPI. ProfileAttribute SPI would allow defining configurable providers for single user attributes. I'm also considering adding a separate Validation SPI, so a ProfileAttribute provider could delegate validation to a separate validator. Users could also implement their own Profile provider to do whatever they want. I'd like to aim to make the SPI a supported SPI. First pass would focus purely on validation. Second pass would focus on using the attribute metadata to do things like: * Have dropdown boxes in mappers to select user attribute instead of copy/pasting the name * Have additional built-in attributes on registration form, update profile form and account management console that can be enabled/disabled by defining the Profile. I'm not suggesting a huge amount here and it will be limited to a few sensible attributes. Defining more complex things like address would still be done through extending the forms.