Return the regenerated token by reading it back at the pushed revision

Motivation:

The regenerated token was passed out of the content transformer through an
AtomicReference, which is an awkward side channel.

Modifications:

- Read the app identity registry back at the revision the push produced and
  return the token from it, instead of capturing the token in the transformer.

Result:

- No behavior change; the caller still always receives the secret its own
  commit produced.

Author: ikhoon

server/src/main/java/com/linecorp/centraldogma/server/metadata/AppIdentityService.java

@@ -33,7 +33,6 @@
 import java.util.Objects;
 import java.util.UUID;
 import java.util.concurrent.CompletableFuture;
-import java.util.concurrent.atomic.AtomicReference;
 
 import org.jspecify.annotations.Nullable;
 
@@ -183,9 +182,6 @@ CompletableFuture<Token> regenerateTokenSecret(Author author, String appId,
 
         final String commitSummary = "Regenerate the secret of the token: " + appId;
 
-        // Capture the regenerated token so that the caller gets the secret this commit produced
-        // even if another commit lands right after this one.
-        final AtomicReference<Token> newTokenRef = new AtomicReference<>();
         final AppIdentityRegistryTransformer transformer = new AppIdentityRegistryTransformer(
                 (headRevision, registry) -> {
                     final AppIdentity appIdentity = registry.get(appId); // Raise an exception if not found.
@@ -228,7 +224,6 @@ CompletableFuture<Token> regenerateTokenSecret(Author author, String appId,
                     final Token newToken = new Token(token.appId(), newSecret, token.isSystemAdmin(),
                                                      token.allowGuestAccess(), token.creation(),
                                                      token.deactivation(), null);
-                    newTokenRef.set(newToken);
                     final Map<String, AppIdentity> newAppIds =
                             updateMap(registry.appIds(), appId, newToken);
                     // A deactivated token has no entry in the secret map, so the new secret is not
@@ -238,9 +233,14 @@ CompletableFuture<Token> regenerateTokenSecret(Author author, String appId,
                             removeFromMap(registry.secrets(), oldSecret);
                     return new AppIdentityRegistry(newAppIds, newSecrets, registry.certificateIds());
                 });
+        // Read the registry back at the revision this commit produced so that the caller gets
+        // the secret of this commit even if another commit lands right after.
         return appIdentityRegistryRepo.push(INTERNAL_PROJECT_DOGMA, Project.REPO_DOGMA, author,
                                             commitSummary, transformer)
-                                      .thenApply(unused -> newTokenRef.get());
+                                      .thenCompose(revision -> appIdentityRegistryRepo.fetch(
+                                              INTERNAL_PROJECT_DOGMA, Project.REPO_DOGMA, TOKEN_JSON,
+                                              revision))
+                                      .thenApply(holder -> (Token) holder.object().get(appId));
     }
 
     CompletableFuture<Revision> activateToken(Author author, String appId) {

server/src/main/java/com/linecorp/centraldogma/server/metadata/RepositorySupport.java

@@ -66,6 +66,13 @@ CompletableFuture<HolderWithRevision<T>> fetch(String projectName, String repoNa
         return fetch(projectManager().get(projectName).repos().get(repoName), path);
     }
 
+    CompletableFuture<HolderWithRevision<T>> fetch(String projectName, String repoName, String path,
+                                                   Revision revision) {
+        requireNonNull(projectName, "projectName");
+        requireNonNull(repoName, "repoName");
+        return fetch(projectManager().get(projectName).repos().get(repoName), path, revision);
+    }
+
     private CompletableFuture<HolderWithRevision<T>> fetch(Repository repository, String path) {
         requireNonNull(path, "path");
         final Revision revision = normalize(repository);