How to check if a user is logged in (how to properly use user.is_authenticated)?

Where and when to authenticate

At the very forefront of view functions destined for authenticated users, a login check must take place. Thanks to @login_required decorator, the view stands as guardian, only letting in those with the golden ticket (authentication).

from django.contrib.auth.decorators import login_required

@login_required
def my_secure_view(request):
    # Psst! If you're not logged, you aren't getting past this point
    # your view code here
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Preferring class-based views (CBV)? Fret not! LoginRequiredMixin is here to help.

Guarding the treasure (Content in templates)

In Django templates, {% if user.is_authenticated %} is your trusty guard, allowing or blocking content based on login status. The user context variable, however, must get a correct pass to the template for this to work.

{% if user.is_authenticated %}
    Welcome {{ user.username }}! <!-- Secret greeting for our members -->
{% else %}
    Please <a href="{% url 'login' %}">log in</a>. <!-- Friendly nudge for the outsiders -->
{% endif %}
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When things seem off, don't forget to ensure the user instance's presence in the context and verify the syntax for typos.

Handling JSON responses

When JsonResponse marries user.is_authenticated, the match isn't always harmonious. As user.is_authenticated is a CallableBool, serialization may be a rocky path. Manual conversion to a common boolean helps avoid any spats:

return JsonResponse({
    "is_authenticated": bool(request.user.is_authenticated)
})
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