Validate server_certs_key_passphrase is 32 chars

Fernet checks[1] for 32 characters long key, so Octavia should validate
the value provided for server_certs_key_passphrase, to reject an invalid
passphrase as early as possible.

This[2] Red Hat Bug showed a case in which an invalid passphrase got
configured, and as a result, Octavia was unable to create any
load balancers.

Related-bug: #1833942

[1] 784676de33/src/cryptography/fernet.py (L36)
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1723051

Change-Id: I334364d4654491bc0d289472ca9ab5fe462d5139
(cherry picked from commit a77667339d)

octavia/certificates/common/local.py

@@ -53,8 +53,10 @@ certgen_opts = [
     cfg.StrOpt('server_certs_key_passphrase',
                default=TLS_PASS_AMPS_DEFAULT,
                help='Passphrase for encrypting Amphora Certificates and '
-                    'Private Keys. Defaults to env[TLS_PASS_AMPS_DEFAULT] or '
-                    'insecure-key-do-not-use-this-key',
+                    'Private Keys. Must be 32, base64(url) compatible, '
+                    'characters long. Defaults to env[TLS_PASS_AMPS_DEFAULT] '
+                    'or insecure-key-do-not-use-this-key',
+               regex=r'^[A-Za-z0-9\-_=]{32}$',
                required=True),
     cfg.StrOpt('signing_digest',
                default=TLS_DIGEST_DEFAULT,

octavia/tests/unit/common/test_config.py

@@ -13,6 +13,7 @@
 #    under the License.
 
 from oslo_config import cfg
+from oslo_config import fixture as oslo_fixture
 
 import octavia.common.config as config
 import octavia.tests.unit.base as base
@@ -26,3 +27,25 @@ class TestConfig(base.TestCase):
         # Resetting because this will cause inconsistent errors when run with
         # other tests
         self.addCleanup(cfg.CONF.reset)
+
+    def test_validate_server_certs_key_passphrase(self):
+        conf = self.useFixture(oslo_fixture.Config(config.cfg.CONF))
+        conf.config(
+            group="certificates",
+            server_certs_key_passphrase="insecure-key-do-not-use-this-key"
+        )
+
+        # Test too short
+        self.assertRaises(ValueError, conf.config,
+                          group="certificates",
+                          server_certs_key_passphrase="short_passphrase")
+
+        # Test too long
+        self.assertRaises(
+            ValueError, conf.config, group="certificates",
+            server_certs_key_passphrase="long-insecure-key-do-not-use-this")
+
+        # Test invalid characters
+        self.assertRaises(
+            ValueError, conf.config, group="certificates",
+            server_certs_key_passphrase="insecure-key-do-not-u$e-this-key")

releasenotes/notes/input-validation-server_certs_key_passphrase-6a9dfc190c9deba8.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - The passphrase for config option 'server_certs_key_passphrase' is used as
+    a Fernet key in Octavia and thus must be 32, base64(url) compatible,
+    characters long. Octavia will now validate the passphrase length and
+    format.