Plone: Add additional registration fields to users (members) - plone

Question

I have two additional fields for my group objects (like described here).
Now I need (other) additional fields for my member objects as well (short strings). I have created them in portal_memberdata/manage_propertiesForm, but I still can't select them for registration form usage (##member-registration).
I need the two new fields for registration, at least one of them mandatory. How can I achieve this? Thank you!
Update:
I found plone.app.users.userdataschema and added my fields to the interface IUserDataSchema; furthermore, I monkeypatched plone.app.users.browser.personalpreferences.UserDataPanelAdapter. There still seems to be missing something (no change visible in ##member-registration).
My customization code looks like this:
from plone.app.users.userdataschema import IUserDataSchema
from zope import schema
from Products.CMFPlone import PloneMessageFactory as _
IUserDataSchema.custom1 = schema.ASCIILine(
title=_(u'label_custom1',
default=u'Custom1 member id'),
description=_(u'help_custom1_creation',
default=u'Custom1 membership is required; '
u'please enter your member id'),
required=True)
from plone.app.users.browser.personalpreferences import UserDataPanelAdapter
def set_custom1(self, value):
if value is None:
value = ''
return self.context.setMemberProperties({'custom1': value})
def get_custom1(self):
return self._getProperty('custom1')
UserDataPanelAdapter.custom1 = property(get_custom1, set_custom1)

Answer 1

It didn't work when I used the monkeypatched original interface class;
but it does work to monkeypatch the UserDataSchemaProvider to return a subclass:
from plone.app.users.userdataschema import IUserDataSchema
from plone.app.users.userdataschema import UserDataSchemaProvider
from zope import schema
from Products.CMFPlone import PloneMessageFactory as _
class IUserDataSchemaExtended(IUserDataSchema):
"""
Extends the userdata schema
by a mandatory field
"""
customField1 = schema.ASCIILine(
title=_(u'label_customField1',
default=u'CustomField1 member id'),
description=_(u'help_customField1_creation',
default=u'CustomField1 membership is required; '
u'please enter your member id'),
required=True)
def getExtendedSchema(self):
return IUserDataSchemaExtended
UserDataSchemaProvider.getSchema = getExtendedSchema
from plone.app.users.browser.personalpreferences import UserDataPanelAdapter
def set_customField1(self, value):
if value is None:
value = ''
return self.context.setMemberProperties({'customField1': value})
def get_customField1(self):
return self._getProperty('customField1')
UserDataPanelAdapter.customField1 = property(get_customField1, set_customField1)
Remarks:
It might be better to simply use customField1 for the translatable title instead of label_customField as the name the field is used when the registration page is quickedited
with Plone 5, it apparently is possible to configure additional userdata fields via XML