Main page footer can be overridden

This allows the footer on the main (index) page to be replaced with custom HTML.

Related to jupyterhub/mybinder.org-deploy#2156

binderhub/app.py

@@ -145,6 +145,16 @@ def _log_level(self):
         config=True,
     )
 
+    main_footer_message = Unicode(
+        "",
+        help="""
+        Override the footer on the main page.
+
+        The value will be inserted "as is". Raw HTML is supported.
+        """,
+        config=True,
+    )
+
     extra_footer_scripts = Dict(
         {},
         help="""
@@ -822,6 +832,7 @@ def initialize(self, *args, **kwargs):
                 "google_analytics_domain": self.google_analytics_domain,
                 "about_message": self.about_message,
                 "banner_message": self.banner_message,
+                "main_footer_message": self.main_footer_message,
                 "extra_footer_scripts": self.extra_footer_scripts,
                 "jinja2_env": jinja_env,
                 "build_memory_limit": self.build_memory_limit,

binderhub/main.py

@@ -36,6 +36,7 @@ def get(self):
             submit=False,
             google_analytics_code=self.settings["google_analytics_code"],
             google_analytics_domain=self.settings["google_analytics_domain"],
+            main_footer_message=self.settings["main_footer_message"],
             extra_footer_scripts=self.settings["extra_footer_scripts"],
             repo_providers=self.settings["repo_providers"],
         )

binderhub/templates/index.html

@@ -195,7 +195,15 @@ <h3 class="text-center">How it works</h3>
 {% endblock main %}
 
 {% block footer %}
+
+{% if main_footer_message %}
+<div class="container">
+  {{ main_footer_message | safe }}
+</div>
+{% else %}
 {{ super () }}
+{% endif %}
+
 <script type="text/javascript">
 indexMain();
 </script>

testing/local-binder-local-hub/binderhub_config.py

@@ -29,6 +29,7 @@
 c.BinderHub.banner_message = (
     'See <a href="https://github.com/jupyterhub/binderhub">BinderHub on GitHub</a>'
 )
+c.BinderHub.main_footer_message = '<div class="row text-center" style="transform:rotate(10deg);padding-top:3em;"><h3>This is a custom footer message.</h3></div>'
 
 c.BinderHub.hub_url_local = "http://localhost:8000"