Be consistent with checking capitalization in rfc2136 plugin (#10188)

Fixes https://github.com/certbot/certbot/issues/10177.

We were using `.upper()` when validating the config but not when
actually creating the object. Now we call it in both places. I updated a
test to work as a regression test here.

certbot-dns-rfc2136/certbot_dns_rfc2136/_internal/dns_rfc2136.py

@@ -91,12 +91,13 @@ class Authenticator(dns_common.DNSAuthenticator):
         if not self.credentials:  # pragma: no cover
             raise errors.Error("Plugin has not been prepared.")
 
+        algorithm: str = (self.credentials.conf('algorithm') or '').upper()
+
         return _RFC2136Client(cast(str, self.credentials.conf('server')),
                               int(cast(str, self.credentials.conf('port')) or self.PORT),
                               cast(str, self.credentials.conf('name')),
                               cast(str, self.credentials.conf('secret')),
-                              self.ALGORITHMS.get(self.credentials.conf('algorithm') or '',
-                                                  dns.tsig.HMAC_MD5),
+                              self.ALGORITHMS.get(algorithm, dns.tsig.HMAC_MD5),
                               (self.credentials.conf('sign_query') or '').upper() == "TRUE")
 
 

certbot-dns-rfc2136/certbot_dns_rfc2136/_internal/tests/dns_rfc2136_test.py

@@ -79,12 +79,17 @@ class AuthenticatorTest(test_util.TempDirTestCase, dns_test_common.BaseAuthentic
             self.auth.perform([self.achall])
 
     @test_util.patch_display_util()
-    def test_valid_algorithm_passes(self, unused_mock_get_utility):
+    @mock.patch('certbot_dns_rfc2136._internal.dns_rfc2136._RFC2136Client')
+    def test_valid_algorithm_passes(self, client, unused_mock_get_utility):
+        from certbot_dns_rfc2136._internal.dns_rfc2136 import Authenticator
+
         config = VALID_CONFIG.copy()
         config["rfc2136_algorithm"] = "HMAC-sha512"
         dns_test_common.write(config, self.config.rfc2136_credentials)
+        self.auth = Authenticator(self.config, "rfc2136")
 
         self.auth.perform([self.achall])
+        assert dns.tsig.HMAC_SHA512 in client.call_args.args
 
     def test_invalid_server_raises(self):
         config = VALID_CONFIG.copy()