GitHubAppCredentials.writeReplace to avoid recalculating tokens

src/main/java/org/jenkinsci/plugins/github_branch_source/GitHubAppCredentials.java

@@ -1,17 +1,20 @@
 package org.jenkinsci.plugins.github_branch_source;
 
 import com.cloudbees.plugins.credentials.CredentialsScope;
+import com.cloudbees.plugins.credentials.CredentialsSnapshotTaker;
 import com.cloudbees.plugins.credentials.common.StandardUsernamePasswordCredentials;
 import com.cloudbees.plugins.credentials.impl.BaseStandardCredentials;
 import edu.umd.cs.findbugs.annotations.CheckForNull;
 import edu.umd.cs.findbugs.annotations.NonNull;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import hudson.Extension;
 import hudson.Util;
+import hudson.remoting.Channel;
 import hudson.util.FormValidation;
 import hudson.util.ListBoxModel;
 import hudson.util.Secret;
 import java.io.IOException;
+import java.io.Serializable;
 import java.util.List;
 import org.kohsuke.accmod.Restricted;
 import org.kohsuke.accmod.restrictions.NoExternalUse;
@@ -165,6 +168,58 @@ public String getUsername() {
         return appID;
     }
 
+    /**
+     * Ensures that the credentials state as serialized via Remoting to an agent includes fields which are {@code transient} for purposes of XStream.
+     * This provides a ~2× performance improvement over reconstructing the object without that state,
+     * in the normal case that {@link #cachedToken} is valid and will remain valid for the brief time that elapses before the agent calls {@link #getPassword}:
+     * <ul>
+     * <li>We do not need to make API calls to GitHub to obtain a new token.
+     * <li>We can avoid the considerable amount of class loading associated with the JWT library, Jackson data binding, Bouncy Castle, etc.
+     * </ul>
+     * @see CredentialsSnapshotTaker
+     */
+    private Object writeReplace() {
+        if (/* XStream */Channel.current() == null) {
+            return this;
+        }
+        return new Replacer(this);
+     }
+
+     private static final class Replacer implements Serializable {
+
+         private final CredentialsScope scope;
+         private final String id;
+         private final String description;
+         private final String appID;
+         private final Secret privateKey;
+         private final String apiUri;
+         private final String owner;
+         private final String cachedToken;
+         private final long tokenCacheTime;
+
+         Replacer(GitHubAppCredentials onMaster) {
+             scope = onMaster.getScope();
+             id = onMaster.getId();
+             description = onMaster.getDescription();
+             appID = onMaster.appID;
+             privateKey = onMaster.privateKey;
+             apiUri = onMaster.apiUri;
+             owner = onMaster.owner;
+             cachedToken = onMaster.cachedToken;
+             tokenCacheTime = onMaster.tokenCacheTime;
+         }
+
+         private Object readResolve() {
+             GitHubAppCredentials clone = new GitHubAppCredentials(scope, id, description, appID, privateKey);
+             clone.apiUri = apiUri;
+             clone.owner = owner;
+             clone.cachedToken = cachedToken;
+             clone.tokenCacheTime = tokenCacheTime;
+             return clone;
+         }
+
+     }
+
     /**
      * {@inheritDoc}
      */