Automate TLS certificates settings for redis backend

This adds support for configuring certificate/key files used for TLS
connection with Redis using the existing tls_* options.

example)

[cache]
backend=dogpile.cache.backend.redis
backend_arguments=url:rediss://:a_big_secret@localhost:2679
tls_enabled=True
tls_cafile = /etc/pki/tls/certs/ca-bundle.crt

Change-Id: I2ab38b8c88274cb4908791eea8212a79e3d524a2

oslo_cache/core.py

@@ -206,6 +206,29 @@ def _build_cache_config(conf):
                 tls_context.set_ciphers(conf.cache.tls_allowed_ciphers)
 
             conf_dict['%s.arguments.tls_context' % prefix] = tls_context
+        elif conf.cache.backend in ('dogpile.cache.redis',):
+            if conf.cache.tls_allowed_ciphers is not None:
+                raise exception.ConfigurationError(
+                    "Limiting allowed ciphers is not supported by "
+                    "the %s backend" % conf.cache.backend)
+            if conf.cache.enforce_fips_mode:
+                raise exception.ConfigurationError(
+                    "FIPS mode is not supported by the %s backend" %
+                    conf.cache.backend)
+
+            conn_kwargs = {}
+            if conf.cache.tls_cafile is not None:
+                _LOG.debug('Oslo Cache TLS - CA: %s', conf.cache.tls_cafile)
+                conn_kwargs['ssl_ca_certs'] = conf.cache.tls_cafile
+            if conf.cache.tls_certfile is not None:
+                _LOG.debug('Oslo Cache TLS - cert: %s',
+                           conf.cache.tls_certfile)
+                _LOG.debug('Oslo Cache TLS - key: %s', conf.cache.tls_keyfile)
+                conn_kwargs.update({
+                    'ssl_certfile': conf.cache.tls_certfile,
+                    'ssl_keyfile': conf.cache.tls_keyfile
+                })
+            conf_dict['%s.arguments.connection_kwargs' % prefix] = conn_kwargs
         else:
             msg = _(
                 "TLS setting via [cache] tls_enabled is not supported by this "

oslo_cache/tests/unit/test_cache_basics.py

@@ -294,6 +294,23 @@ class CacheRegionTest(test_cache.BaseTestCase):
             ssl.create_default_context.assert_not_called()
             self.assertNotIn('test_prefix.arguments.tls_context', config_dict)
 
+    def test_cache_dictionary_config_builder_tls_disabled_redis(self):
+        """Validate the backend is reset to default if caching is disabled."""
+        self.config_fixture.config(group='cache',
+                                   enabled=True,
+                                   config_prefix='test_prefix',
+                                   backend='dogpile.cache.redis',
+                                   tls_cafile='path_to_ca_file',
+                                   tls_keyfile='path_to_key_file',
+                                   tls_certfile='path_to_cert_file',
+                                   tls_allowed_ciphers='allowed_ciphers')
+
+        config_dict = cache._build_cache_config(self.config_fixture.conf)
+
+        self.assertFalse(self.config_fixture.conf.cache.tls_enabled)
+        self.assertNotIn('test_prefix.arguments.connection_kwargs',
+                         config_dict)
+
     def test_cache_dictionary_config_builder_tls_enabled(self):
         """Validate the backend is reset to default if caching is disabled."""
         self.config_fixture.config(group='cache',
@@ -318,6 +335,30 @@ class CacheRegionTest(test_cache.BaseTestCase):
                 config_dict['test_prefix.arguments.tls_context'],
             )
 
+    def test_cache_dictionary_config_builder_tls_enabled_redis(self):
+        """Validate the backend is reset to default if caching is disabled."""
+        self.config_fixture.config(group='cache',
+                                   enabled=True,
+                                   config_prefix='test_prefix',
+                                   backend='dogpile.cache.redis',
+                                   tls_enabled=True,
+                                   tls_cafile='path_to_ca_file',
+                                   tls_keyfile='path_to_key_file',
+                                   tls_certfile='path_to_cert_file')
+
+        config_dict = cache._build_cache_config(self.config_fixture.conf)
+
+        self.assertTrue(self.config_fixture.conf.cache.tls_enabled)
+        self.assertIn('test_prefix.arguments.connection_kwargs',
+                      config_dict)
+        self.assertEqual(
+            {
+                'ssl_ca_certs': 'path_to_ca_file',
+                'ssl_keyfile': 'path_to_key_file',
+                'ssl_certfile': 'path_to_cert_file'
+            },
+            config_dict['test_prefix.arguments.connection_kwargs'])
+
     @mock.patch('oslo_cache.core._LOG')
     def test_cache_dictionary_config_builder_fips_mode_supported(self, log):
         """Validate the FIPS mode is supported."""
@@ -357,6 +398,19 @@ class CacheRegionTest(test_cache.BaseTestCase):
                               cache._build_cache_config,
                               self.config_fixture.conf)
 
+    def test_cache_dictionary_config_builder_fips_mode_unsupported_redis(self):
+        """Validate the FIPS mode is not supported."""
+        self.config_fixture.config(group='cache',
+                                   enabled=True,
+                                   config_prefix='test_prefix',
+                                   backend='dogpile.cache.redis',
+                                   tls_enabled=True,
+                                   enforce_fips_mode=True)
+
+        self.assertRaises(exception.ConfigurationError,
+                          cache._build_cache_config,
+                          self.config_fixture.conf)
+
     def test_cache_dictionary_config_builder_tls_enabled_unsupported(self):
         """Validate the tls_enabled opiton is not supported.."""
         self.config_fixture.config(group='cache',

releasenotes/notes/redis-ssl-ca14b4b99c2e5a84.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    When the ``dogpile.cache.redis`` backend is used and
+    the ``[cache] tls_enable`` option is set to True, now the following
+    ``[cache]`` options set tls certificates and keys used for TLS
+    communication with Redis.
+
+    - ``tls_cafile``
+    - ``tls_certfile``
+    - ``tls_keyfile``