Use luci-config for infrequently changing settings, part 2.

appengine/auth_service/handlers_frontend.py

Index: appengine/auth_service/handlers_frontend.py
diff --git a/appengine/auth_service/handlers_frontend.py b/appengine/auth_service/handlers_frontend.py
index 1ea9bb77da1b0c0848098c1b5b48a52478dc1bc3..6c7bde5745df3eed9d8c40b6932870447a19a020 100644
--- a/appengine/auth_service/handlers_frontend.py
+++ b/appengine/auth_service/handlers_frontend.py
@@ -94,16 +94,16 @@ class ImporterConfigHandler(auth.ApiHandler):
 
   @auth.require(auth.is_admin)
   def get(self):
-    self.send_response({'config': importer.read_config()})
+    self.send_response({'config': importer.read_config_text()})
 
   @auth.require(auth.is_admin)
   def post(self):
     if config.is_remote_configured():
       self.abort_with_error(409, text='The configuration is managed elsewhere')
-    conf = self.parse_body().get('config')
-    if not importer.is_valid_config(conf):
-      self.abort_with_error(400, text='Invalid config format.')
-    importer.write_config(conf)
+    try:
+      importer.write_config_text(self.parse_body().get('config'))
+    except ValueError as ex:
+      self.abort_with_error(400, text=str(ex))
     self.send_response({'ok': True})