add external oauth example

examples/external-oauth/jupyterhub_config.py

@@ -0,0 +1,17 @@
+import os
+
+# get the oauth client's API token.
+# this could come from anywhere
+api_token = os.getenv("JUPYTERHUB_API_TOKEN")
+if not api_token:
+    raise ValueError("Make sure to `export JUPYTERHUB_API_TOKEN=$(openssl rand -hex 32)`")
+
+# tell JupyterHub to register the service as an external oauth client
+c.JupyterHub.services = [
+    {
+        'name': 'external-oauth',
+        'oauth_client_id': "whoami-oauth-client-test",
+        'api_token': api_token,
+        'oauth_redirect_uri': 'http://127.0.0.1:5555/oauth_callback',
+    },
+]