auth_oidc: select from existing attributes in admin provider page (#37871)

src/authentic2_auth_oidc/admin.py

@@ -16,6 +16,7 @@
 
 from django import forms
 from django.contrib import admin
+from django.forms.widgets import Select
 
 from authentic2.attributes_ng.engine import get_attribute_names
 from authentic2.forms.widgets import DatalistTextInput
@@ -37,6 +38,8 @@ class OIDCClaimMappingForm(forms.ModelForm):
                 'updated_at')
         claim_widget.name = 'list__oidcclaim-mapping-inline'
         claim_widget.attrs.update({'list': 'list__oidcclaim-mapping-inline'})
+        attribute_widget = self.fields['attribute'].widget
+        attribute_widget.choices = [(name, desc) for name, desc in get_attribute_names({})]
 
     class Meta:
         model = models.OIDCClaimMapping
@@ -46,6 +49,7 @@ class OIDCClaimMappingForm(forms.ModelForm):
         readonly_fields = ['created', 'modified']
         widgets = {
             'claim': DatalistTextInput,
+            'attribute': Select,
         }