Remove usage of oslo.config global

Currently application that doesn't use the global configuration object
have to rely on hack to setup the global oslo config object for each middleware
it want to use.

For example, gnocchi have its own middleware loader and add crap to load
keystonemiddleware:

  https://github.com/openstack/gnocchi/blob/master/gnocchi/rest/app.py#L140

And it can't use oslo.middleware that relies on the global conf object.

Also aodh (use 'paste' for middleware) have to hack the global
configuration object for each middlewares it want to use by code...

  https://review.openstack.org/#/c/208632/1/aodh/service.py

But middleware are optional deployer stuffs, we should not write any
code for them...

This change allows application to use paste-deploy (or any middleware
loader) without enforcing the application to use the global oslo.config object.

If the middleware want to use oslo.config it should load the
configuration file himself (and fallback to the global one if any)

The proposed paste configuration to allow this is:

  [filter:cors]
  paste.filter_factory = oslo.middleware:cors
  oslo_config_project = aodh

So the cors middleware can find and load the aodh config and
what is it interested in.

Also, some of them use oslo.config local, some other the global object.
Some can be loaded by an middleware loader like paste, some other not.

This change make consistent the way we bootstrap all middlewares.

Closes-bug: #1482086

Change-Id: Iad197d1f3a386683d818b59718df34e14e15ca5c

3 files changed, 13 insertions, 11 deletions

diff --git a/oslo_middleware/tests/test_cors.py b/oslo_middleware/tests/test_cors.py
index d078d14..8eebf5b 100644
--- a/oslo_middleware/tests/test_cors.py
+++ b/oslo_middleware/tests/test_cors.py
@@ -115,6 +115,9 @@ class CORSTestFilterFactory(test_base.BaseTestCase):
     """Test the CORS filter_factory method."""
 
     def test_filter_factory(self):
+        config = self.useFixture(fixture.Config())
+        config.conf([])
+
         # Test a valid filter.
         filter = cors.filter_factory(None,
                                      allowed_origin='http://valid.example.com',
diff --git a/oslo_middleware/tests/test_sizelimit.py b/oslo_middleware/tests/test_sizelimit.py
index 2a24659..dc29cd0 100644
--- a/oslo_middleware/tests/test_sizelimit.py
+++ b/oslo_middleware/tests/test_sizelimit.py
@@ -78,15 +78,15 @@ class TestRequestBodySizeLimiter(test_base.BaseTestCase):
 
     def setUp(self):
         super(TestRequestBodySizeLimiter, self).setUp()
-        fixture = self.useFixture(config.Config(sizelimit.CONF))
-        self.MAX_REQUEST_BODY_SIZE = \
-            fixture.conf.oslo_middleware.max_request_body_size
+        self.useFixture(config.Config())
 
         @webob.dec.wsgify()
         def fake_app(req):
             return webob.Response(req.body)
 
         self.middleware = sizelimit.RequestBodySizeLimiter(fake_app)
+        self.MAX_REQUEST_BODY_SIZE = (
+            self.middleware.oslo_conf.oslo_middleware.max_request_body_size)
         self.request = webob.Request.blank('/', method='POST')
 
     def test_content_length_acceptable(self):
diff --git a/oslo_middleware/tests/test_ssl.py b/oslo_middleware/tests/test_ssl.py
index 7314260..a94e4c4 100644
--- a/oslo_middleware/tests/test_ssl.py
+++ b/oslo_middleware/tests/test_ssl.py
@@ -13,7 +13,6 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
-from oslo_config import cfg
 from oslo_config import fixture as config
 from oslotest import base
 import webob
@@ -27,8 +26,12 @@ class SSLMiddlewareTest(base.BaseTestCase):
         super(SSLMiddlewareTest, self).setUp()
         self.useFixture(config.Config())
 
-    def _test_scheme(self, expected, headers):
+    def _test_scheme(self, expected, headers, config=None):
         middleware = ssl.SSLMiddleware(None)
+        if config:
+            middleware.oslo_conf.set_override(
+                'secure_proxy_ssl_header', config,
+                group='oslo_middleware')
         request = webob.Request.blank('http://example.com/', headers=headers)
 
         # Ensure ssl middleware does not stop pipeline execution
@@ -44,13 +47,9 @@ class SSLMiddlewareTest(base.BaseTestCase):
         self._test_scheme('https', headers)
 
     def test_with_custom_header(self):
-        cfg.CONF.set_override('secure_proxy_ssl_header', 'X-My-Header',
-                              group='oslo_middleware')
         headers = {'X-Forwarded-Proto': 'https'}
-        self._test_scheme('http', headers)
+        self._test_scheme('http', headers, config='X-My-Header')
 
     def test_with_custom_header_and_forwarded_protocol(self):
-        cfg.CONF.set_override('secure_proxy_ssl_header', 'X-My-Header',
-                              group='oslo_middleware')
         headers = {'X-My-Header': 'https'}
-        self._test_scheme('https', headers)
+        self._test_scheme('https', headers, config='X-My-Header')