class LoginForm(forms.Form):
    username = forms.CharField(label='Введите Ваш логин')
    password = forms.CharField(label='Введите Ваш пароль', widget=forms.PasswordInput)

    def clean(self):
        cleaned_data = super(LoginForm, self).clean()
        username = self.cleaned_data['username']
        password = self.cleaned_data['password']
        if not User.objects.filter(username=username).exists():
            raise forms.ValidationError('Пользователь с таким логином не зарегистрирован!')


        user = User.objects.get(username=username)
        if user and not user.check_password(password):
            raise forms.ValidationError('Неверный пароль!')

def login_view(request):

    if request.method == 'POST':
        form = LoginForm(request.POST)

        if form.is_valid():
            username = form.cleaned_data['username']
            password = form.cleaned_data['password']
            login_user = authenticate(username=username, password=password)
            if login_user:
                login(request, login_user)
                return redirect('/')
    else:
        form = LoginForm()
    return render(request, 'registration/login_view.html', {'form': form})

{% extends 'base.html' %}
{% block content %}
<div class="title">Вход</div>
<section id="login" class="border">
  <form id="login-form" action="" method="POST">
    {% csrf_token %}
    {% for field in form %}
    {{ field.errors }}

    <ul>
      <li>{{ field.label }} *</li>
      <li>
        <input class="input" name="{{ field.name }}" type="{{ field.name }}" /> </li>
    </ul>
    {% endfor %}
    <div>
      <span><input class="block" type="submit" value="Войти" /></span>
    </div>
  </form>
</section>
{% endblock content %}

{% extends 'base.html' %}
{% block content %}
<div class="title">Вход</div>
<section id="login" class="border">
  <form id="login-form" action="" method="POST">
    {% csrf_token %}
    {{ form.non_field_errors }}
    {% for field in form %}
    <ul>
      <li>{{ field.label }} *</li>
      <li>
        <input class="input" name="{{ field.name }}" type="{{ field.name }}" /> </li>
    </ul>
    {% endfor %}
    <div>
      <span><input class="block" type="submit" value="Войти" /></span>
    </div>
  </form>
</section>
{% endblock content %}