Use time-constant comparison in password testing (#3090)

Normal comparison exits out once a difference is found so theoretically
a time variance can leak information. This isn't really a huge deal but
is probably still worth doing.

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

@@ -44,6 +44,8 @@ import google.registry.model.eppcommon.StatusValue;
 import google.registry.model.host.Host;
 import google.registry.model.transfer.TransferStatus;
 import google.registry.persistence.VKey;
+import java.nio.charset.StandardCharsets;
+import java.security.MessageDigest;
 import java.time.Instant;
 import java.util.List;
 import java.util.Objects;
@@ -134,7 +136,9 @@ public final class ResourceFlowUtils {
     }
     String authPassword = authInfo.getPw().getValue();
     String domainPassword = domain.getAuthInfo().getPw().getValue();
-    if (!domainPassword.equals(authPassword)) {
+    if (!MessageDigest.isEqual(
+        authPassword.getBytes(StandardCharsets.UTF_8),
+        domainPassword.getBytes(StandardCharsets.UTF_8))) {
       throw new BadAuthInfoForResourceException();
     }
   }

core/src/main/java/google/registry/security/XsrfTokenManager.java

@@ -25,6 +25,7 @@ import com.google.common.hash.Hashing;
 import google.registry.model.server.ServerSecret;
 import google.registry.util.Clock;
 import jakarta.inject.Inject;
+import java.security.MessageDigest;
 import java.time.Duration;
 import java.time.Instant;
 import java.util.List;
@@ -102,7 +103,7 @@ public final class XsrfTokenManager {
     }
     // Reconstruct the token to verify validity.
     String reconstructedToken = encodeToken(ServerSecret.get().asBytes(), email, timestampMillis);
-    if (!token.equals(reconstructedToken)) {
+    if (!MessageDigest.isEqual(token.getBytes(UTF_8), reconstructedToken.getBytes(UTF_8))) {
       logger.atWarning().log(
           "Reconstructed XSRF mismatch (got != expected): %s != %s", token, reconstructedToken);
       return false;