Add clientCertificate to TlsCredentials.toString() (#945)

* Add clientCertificate to TlsCredentials.toString()

FlowRunner.run() logs these credentials to the GAE logs by implicitly using the
toString() method, so we need to add it if we want it to appear in the logs.

core/src/main/java/google/registry/flows/TlsCredentials.java

@@ -223,6 +223,7 @@ public class TlsCredentials implements TransportCredentials {
   @Override
   public String toString() {
     return toStringHelper(getClass())
+        .add("clientCertificate", clientCertificate.orElse(null))
         .add("clientCertificateHash", clientCertificateHash.orElse(null))
         .add("clientAddress", clientInetAddr.orElse(null))
         .toString();

core/src/test/java/google/registry/flows/FlowRunnerTest.java

@@ -155,12 +155,14 @@ class FlowRunnerTest {
         new TlsCredentials(
             true,
             Optional.of("abc123def"),
-            Optional.of("cert"),
+            Optional.of("cert046F5A3"),
             Optional.of("127.0.0.1"),
             certificateChecker);
     flowRunner.run(eppMetricBuilder);
     assertThat(Splitter.on("\n\t").split(findFirstLogMessageByPrefix(handler, "EPP Command\n\t")))
-        .contains("TlsCredentials{clientCertificateHash=abc123def, clientAddress=/127.0.0.1}");
+        .contains(
+            "TlsCredentials{clientCertificate=cert046F5A3, clientCertificateHash=abc123def,"
+                + " clientAddress=/127.0.0.1}");
   }
 
   @Test