allianceauth/allianceauth/authentication/templates/public/login.html

{% extends 'public/middle_box.html' %}
{% load static %}
{% block title %}Login{% endblock %}
{% block middle_box_content %}
    <p style="text-align:center">
        <a href="{% url 'auth_sso_login' %}">
            <img src="{% static 'img/sso/EVE_SSO_Login_Buttons_Large_Black.png' %}" border=0>
        </a>
    </p>
{% endblock %}