Refs #29379 -- Moved autocomplete attribute to UsernameField.

Moving the autocomplete attribute into UsernameField allows this to work
for custom forms making use of UsernameField, removes some duplication
in the code, and keeps consistency with the autocapitalize attribute
that is already defined on UsernameField.

django/contrib/auth/forms.py

@@ -62,9 +62,11 @@ def to_python(self, value):
         return unicodedata.normalize('NFKC', super().to_python(value))
 
     def widget_attrs(self, widget):
-        attrs = super().widget_attrs(widget)
-        attrs['autocapitalize'] = 'none'
-        return attrs
+        return {
+            **super().widget_attrs(widget),
+            'autocapitalize': 'none',
+            'autocomplete': 'username',
+        }
 
 
 class UserCreationForm(forms.ModelForm):
@@ -96,10 +98,7 @@ class Meta:
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         if self._meta.model.USERNAME_FIELD in self.fields:
-            self.fields[self._meta.model.USERNAME_FIELD].widget.attrs.update({
-                'autocomplete': 'username',
-                'autofocus': True,
-            })
+            self.fields[self._meta.model.USERNAME_FIELD].widget.attrs.update({'autofocus': True})
 
     def clean_password2(self):
         password1 = self.cleaned_data.get("password1")
@@ -166,7 +165,7 @@ class AuthenticationForm(forms.Form):
     Base class for authenticating users. Extend this to get a form that accepts
     username/password logins.
     """
-    username = UsernameField(widget=forms.TextInput(attrs={'autocomplete': 'username', 'autofocus': True}))
+    username = UsernameField(widget=forms.TextInput(attrs={'autofocus': True}))
     password = forms.CharField(
         label=_("Password"),
         strip=False,