Execute these steps one by one:

1. Create the view that will require authentication to download a file, as follows:

# myproject/apps/ideas/views.py
import os

from django.contrib.auth.decorators import login_required
from django.http import FileResponse, HttpResponseNotFound
from django.shortcuts import get_object_or_404
from django.utils.text import slugify

from .models import Idea


@login_required
def download_idea_picture(request, pk):
    idea = get_object_or_404(Idea, pk=pk)
    if idea.picture:
        filename, extension = 
        os.path.splitext(idea.picture.file.name)
        extension = extension[1:] # remove the dot
        response = FileResponse(
            idea.picture.file, content_type=f"image/{extension}"
        )
        slug = slugify(idea.title)[:100]
        response["Content-Disposition"] = (
            "attachment; filename="
            f"{slug}.{extension}"
        )
    else:
        response = HttpResponseNotFound(
            content="Picture unavailable"
        )
    return response

2. Add the download view to the URL configuration:
   

# myproject/apps/ideas/urls.py
from django.urls import path

from .views import download_idea_picture

urlpatterns = [
    # …
    path(
        "<uuid:pk>/download-picture/",
        download_idea_picture,
        name="download_idea_picture",
    ),
]

3. Set up the login view in our project URL configuration:
   

# myproject/urls.py
from django.conf.urls.i18n import i18n_patterns
from django.urls import include, path

urlpatterns = i18n_patterns(
    # …
    path("accounts/", include("django.contrib.auth.urls")),
    path("ideas/", include(("myproject.apps.ideas.urls", "ideas"), 
     namespace="ideas")),
)

4. Create a template for the login form, as shown in the following code:
   

{# registration/login.html #}
{% extends "base.html" %}
{% load i18n %}

{% block content %}
    <h1>{% trans "Login" %}</h1>
    <form action="{{ request.path }}" method="POST">
        {% csrf_token %}
        {{ form.as_p }}
        <button type="submit" class="btn btn-primary">{% trans 
         "Log in" %}</button>
    </form>
{% endblock %}

5. In the template of idea details, add a link to the download:

{# ideas/idea_detail.html #}
{% extends "base.html" %}
{% load i18n %}

{% block content %}
…
    <a href="{% url 'ideas:download_idea_picture' pk=idea.pk %}" 
     class="btn btn-primary">{% trans "Download picture" %}</a>
{% endblock %}

You should restrict users from bypassing Django and downloading restricted files directly. To do so, on an Apache web server, you can put a .htaccess file in the media/ideas directory by using the following content if you are running Apache 2.4:

# media/ideas/.htaccess
Require all denied