自定义Django登录模板的错误字段

from django.contrib.auth.forms import AuthenticationForm

class CustomLoginForm(AuthenticationForm):
    error_messages = {
        'username': {
            'required': '请填写用户名。',
            'invalid': '用户名格式不正确。',
        },
        'password': {
            'required': '请填写密码。',
        },
    }

from django.contrib.auth.views import LoginView
from .forms import CustomLoginForm

class CustomLoginView(LoginView):
    form_class = CustomLoginForm
    template_name = 'login.html'

<form method="post">
  {% csrf_token %}
  {{ form.username.errors }}
  <label for="{{ form.username.id_for_label }}">用户名:</label>
  {{ form.username }}
  <br>
  {{ form.password.errors }}
  <label for="{{ form.password.id_for_label }}">密码:</label>
  {{ form.password }}
  <br>
  <input type="submit" value="登录">
</form>