Add a Date to Userschema

Hi, I'm building an addon that extends the userschema with a Date field. When I set that field in volto, it ends up as a string value in the user properties in plone . I tried converting it to a date in a handler of Products.PluggableAuthService.interfaces.events.IPropertiesUpdatedEvent but it gets changed back to string after the handler completes. I can get it work by monkey patching the UsersPatch's reply method here but I was hoping there's a nicer option.

I tried to create a custom deserializer for plone.app.users.schema.IUserDataSchema but Icannot get it to fire:

<adapter
factory=".deserializer.CustomUserFieldDeserializer"
for="plone.app.users.schema.IUserDataSchema

      zope.interface.Interface"
provides="plone.restapi.interfaces.IFieldDeserializer"

/>

Has anyone extended their userschema with a Date?