Mark noauth authentication as deprecated

Change-Id: Iac5a286ed171b5be303b8c4ba8ad1e2a4071cbf9

gnocchi/rest/app.py

@@ -15,6 +15,7 @@
 # under the License.
 import os
 import uuid
+import warnings
 
 from oslo_config import cfg
 from oslo_log import log
@@ -107,6 +108,11 @@ def load_app(conf, indexer=None, storage=None,
     APPCONFIGS[configkey] = config
 
     LOG.info("WSGI config used: %s", cfg_path)
+
+    if conf.api.auth_mode == "noauth":
+        warnings.warn("The `noauth' authentication mode is deprecated",
+                      category=DeprecationWarning)
+
     appname = "gnocchi+" + conf.api.auth_mode
     app = deploy.loadapp("config:" + cfg_path, name=appname,
                          global_conf={'configkey': configkey})

releasenotes/notes/deprecate-noauth-01b7e961d9a17e9e.yaml

@@ -0,0 +1,4 @@
+---
+deprecations:
+  - The `noauth` authentication mechanism is deprecated and will be removed in
+    a next version.