Add login form for admin that uses OIDC

{{ cookiecutter.project_slug }}/src/{{ cookiecutter.project_slug }}/core/admin.py

@@ -4,3 +4,4 @@
 from . import models
 
 admin.site.register(models.MafiasiUser, UserAdmin)
+admin.site.login_template = 'core/login.html'

{{ cookiecutter.project_slug }}/src/{{ cookiecutter.project_slug }}/core/templates/core/login.html

@@ -0,0 +1,22 @@
+{% extends "admin/login.html" %}
+{% load i18n %}
+{% block content %}
+<div id="content-main">
+
+{% if user.is_authenticated %}
+<p class="errornote">
+{% blocktranslate trimmed %}
+    You are authenticated as {{ username }}, but are not authorized to
+    access this page. Would you like to login to a different account?
+{% endblocktranslate %}
+</p>
+{% endif %}
+
+<form id="login-form" method="get" action="{% url 'simple_openid_connect:login' %}">
+  <div class="submit-row">
+    <input type="submit" value="Log in with Mafiasi">
+  </div>
+</form>
+
+</div>
+{% endblock %}