I'm trying to do the Login for my Django (2.0) website, so far I've got the login working for existing accounts. I'm using the built-in login function.

Now I want to display an error message when you enter an invalid account, for example "Invalid username or password!". But I have no idea how to go about this.

Right now it just refreshes the login page when your enter an invalid account. Any help is appreciated!

Login.html

{% block title %}Login{% endblock %}

{% block content %}
  <h2>Login</h2>
  <form method="post">
    {% csrf_token %}
    {{ form.as_p }}
    <button type="submit">Login</button>
  </form>
{% endblock %}

Login view

def login(request):
    if request.method == 'POST':
        form = AuthenticationForm(request.POST)
        username = request.POST['username']
        password = request.POST['password']
        user = authenticate(username=username, password=password)

        if user is not None:
            if user.is_active:
                auth_login(request, user)
                return redirect('index')

    else:
        form = AuthenticationForm()
    return render(request, 'todo/login.html', {'form': form})

in your template

{% for message in messages %}
    
    <div class="alert alert-success">
        <a class="close" href="#" data-dismiss="alert">×</a>
           {{ message }}
    </div>

{% endfor %}

in view

from django.contrib import messages

def login(request):
    if request.method == 'POST':
        form = AuthenticationForm(request.POST)
        username = request.POST['username']
        password = request.POST['password']
        user = authenticate(username=username, password=password)
    
        if user is not None:
            if user.is_active:
                auth_login(request, user)
                return redirect('index')
        else:
            messages.error(request,'username or password not correct')
            return redirect('login')
    
    else:
        form = AuthenticationForm()
    return render(request, 'todo/login.html', {'form': form})