Merge pull request #291 from jglick/GitHubAppCredentials.cachedToken

Cache app installation token

Author: bitwiseman

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

@@ -5,6 +5,7 @@
 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.util.FormValidation;
@@ -27,6 +28,7 @@
 import static org.jenkinsci.plugins.github_branch_source.GitHubSCMNavigator.DescriptorImpl.getPossibleApiUriItems;
 import static org.jenkinsci.plugins.github_branch_source.JwtHelper.createJWT;
 
+@SuppressFBWarnings(value = "SE_NO_SERIALVERSIONID", justification = "XStream")
 public class GitHubAppCredentials extends BaseStandardCredentials implements StandardUsernamePasswordCredentials {
 
     private static final String ERROR_AUTHENTICATING_GITHUB_APP = "Couldn't authenticate with GitHub app ID %s";
@@ -44,6 +46,9 @@ public class GitHubAppCredentials extends BaseStandardCredentials implements Sta
 
     private String owner;
 
+    private transient String cachedToken;
+    private transient long tokenCacheTime;
+
     @DataBoundConstructor
     @SuppressWarnings("unused") // by stapler
     public GitHubAppCredentials(
@@ -138,7 +143,15 @@ public Secret getPassword() {
             apiUri = "https://api.github.com";
         }
 
-        String appInstallationToken = generateAppInstallationToken(appID, privateKey.getPlainText(), apiUri, owner);
+        long now = System.currentTimeMillis();
+        String appInstallationToken;
+        if (cachedToken != null && now - tokenCacheTime < JwtHelper.VALIDITY_MS /* extra buffer */ / 2) {
+            appInstallationToken = cachedToken;
+        } else {
+            appInstallationToken = generateAppInstallationToken(appID, privateKey.getPlainText(), apiUri, owner);
+            cachedToken = appInstallationToken;
+            tokenCacheTime = now;
+        }
 
         return Secret.fromString(appInstallationToken);
     }

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

@@ -10,12 +10,17 @@
 import java.security.spec.PKCS8EncodedKeySpec;
 import java.util.Base64;
 import java.util.Date;
-import java.util.Objects;
 
 import static java.util.Objects.requireNonNull;
+import java.util.concurrent.TimeUnit;
 
 class JwtHelper {
 
+    /**
+     * Somewhat less than the <a href="https://developer.github.com/apps/building-github-apps/authenticating-with-github-apps/#authenticating-as-a-github-app">maximum JWT validity</a>.
+     */
+    static final long VALIDITY_MS = TimeUnit.MINUTES.toMillis(8);
+
     /**
      * Create a JWT for authenticating to GitHub as an app installation
      * @param githubAppId the app ID
@@ -42,9 +47,7 @@ static String createJWT(String githubAppId, final String privateKey) {
                 .setIssuer(githubAppId)
                 .signWith(signingKey, signatureAlgorithm);
 
-        long oneMinuteInMillis = 60L * 1000L;
-        long expMillis = nowMillis + (oneMinuteInMillis * 8);
-        Date exp = new Date(expMillis);
+        Date exp = new Date(nowMillis + VALIDITY_MS);
         builder.setExpiration(exp);
 
         return builder.compact();