Display error message when login fails in Django

Django:1.10

I want to display an error message when login fails with the authentication system provided by Django.

Apparently, you can use Form's add_error.

The Forms API | Django documentation | Django https://docs.djangoproject.com/en/1.10/ref/forms/api/#django.forms.Form.add_error

Prepare a form,

forms.py

from django import forms

class LoginForm(forms.Form):
    username = forms.CharField(label='LOGIN_ID', max_length=30)
    password = forms.CharField(
            label='PASSWORD', max_length=128, widget=forms.PasswordInput())

Add_error to form in view

views.py

from django.contrib.auth import authenticate, login
from django.shortcuts import get_object_or_404, redirect, render

from .forms import LoginForm

def user_login(request):
    form = LoginForm()
    return render(request, 'polls/login.html', {'form': form})

def authentication(request):
    form = LoginForm(request.POST)
    if form.is_valid():
        username = form.cleaned_data['username']
        password = form.cleaned_data['password']
        user = authenticate(username=username, password=password)
        if user is not None:
            if user.is_active:
                login(request, user)
                return redirect('polls:index')
    form.add_error(None, 'LOGIN_The ID or PASSWORD is different.')
    return render(request, 'polls/login.html', {'form': form})

Just make the template show the error message. (Because the first argument of add_error is NONE, it is obtained from non_field_errors)

login.html

・ ・ ・
{% for error in form.non_field_errors %}
    <p>{{ error }}</p>
{% endfor %}
・ ・ ・

It was displayed like this.