EmailAuthUserAdmin

from django.contrib import admin
from django.contrib.auth.models import User
from django.contrib.auth.admin import UserAdmin
from django.contrib.auth.forms import UserChangeForm
from django import forms

class EmailUserChangeForm(UserChangeForm):
    username = forms.EmailField(label='Username')

class EmailUserAdmin(UserAdmin):
    form = EmailUserChangeForm

admin.site.unregister(User)
admin.site.register(User, EmailUserAdmin)