Set a cookie for /admin/munin pages to grant access to Munin reports

The /admin/munin routes used the same Authorization: header logic as the other API routes, but they are browsed directly in the browser because they are handled as static pages or as a proxy to a CGI script.

This required users to enter their email username/password for HTTP basic authentication in the standard browser auth prompt, which wasn't ideal (and may leak the password in browser storage). It also stopped working when MFA was enabled for user accounts.

A token is now set in a cookie when visiting /admin/munin which is then checked in the routes that proxy the Munin pages. The cookie's lifetime is kept limited to limit the opportunity for any unknown CSRF attacks via the Munin CGI script.

management/daemon.py

@@ -654,16 +654,42 @@ def privacy_status_set():
 # MUNIN
 
 @app.route('/munin/')
-@app.route('/munin/<path:filename>')
 @authorized_personnel_only
-def munin(filename=""):
-	# Checks administrative access (@authorized_personnel_only) and then just proxies
-	# the request to static files.
+def munin_start():
+	# Munin pages, static images, and dynamically generated images are served
+	# outside of the AJAX API. We'll start with a 'start' API that sets a cookie
+	# that subsequent requests will read for authorization. (We don't use cookies
+	# for the API to avoid CSRF vulnerabilities.)
+	response = make_response("OK")
+	response.set_cookie("session", auth_service.create_session_key(request.user_email, env, type='cookie'),
+	    max_age=60*30, secure=True, httponly=True, samesite="Strict") # 30 minute duration
+	return response
+
+def check_request_cookie_for_admin_access():
+	session = auth_service.get_session(None, request.cookies.get("session", ""), "cookie", env)
+	if not session: return False
+	privs = get_mail_user_privileges(session["email"], env)
+	if not isinstance(privs, list): return False
+	if "admin" not in privs: return False
+	return True
+
+def authorized_personnel_only_via_cookie(f):
+	@wraps(f)
+	def g(*args, **kwargs):
+		if not check_request_cookie_for_admin_access():
+			return Response("Unauthorized", status=403, mimetype='text/plain', headers={})
+		return f(*args, **kwargs)
+	return g
+
+@app.route('/munin/<path:filename>')
+@authorized_personnel_only_via_cookie
+def munin_static_file(filename=""):
+	# Proxy the request to static files.
 	if filename == "": filename = "index.html"
 	return send_from_directory("/var/cache/munin/www", filename)
 
 @app.route('/munin/cgi-graph/<path:filename>')
-@authorized_personnel_only
+@authorized_personnel_only_via_cookie
 def munin_cgi(filename):
 	""" Relay munin cgi dynazoom requests
 	/usr/lib/munin/cgi/munin-cgi-graph is a perl cgi script in the munin package