Add authentication from upstream providers (#107)

Let BasicOIDC delegate authentication to upstream providers (Google, GitHub, GitLab, Keycloak...)

Reviewed-on: #107

templates/settings/providers_list.html

@@ -0,0 +1,39 @@
+{% extends "base_settings_page.html" %}
+{% block content %}
+
+<style>
+#providers td {
+    vertical-align: middle;
+}
+</style>
+
+<table id="providers" class="table table-hover" style="max-width: 800px;" aria-describedby="OpenID providers list">
+    <thead>
+    <tr>
+        <th scope="col"></th>
+        <th scope="col">ID</th>
+        <th scope="col">Name</th>
+        <th scope="col">Configuration URL</th>
+        <th scope="col">Client ID</th>
+    </tr>
+    </thead>
+    <tbody>
+    {% for c in providers %}
+    <tr>
+        <td>
+            <img src="{{ c.logo_url() }}" alt="{{ c.name }} logo" width="30px"/>
+        </td>
+        <td>{{ c.id.0 }}</td>
+        <td>{{ c.name }}</td>
+        <td><a href="{{ c.configuration_url }}" target="_blank" rel="noreferrer">
+            {{ c.configuration_url }}
+        </a></td>
+        <td>{{ c.client_id }}</td>
+    </tr>
+    {% endfor %}
+    </tbody>
+</table>
+
+<p>Redirect URL for new clients: {{ redirect_url }}</p>
+
+{% endblock content %}