OAUth2Client: defer initial token fetch when user interaction is requ…

…ired

api/client/src/main/java/org/projectnessie/client/auth/oauth2/OAuth2Client.java

@@ -54,6 +54,7 @@ class OAuth2Client implements OAuth2Authenticator, Closeable {
   private final HttpClient httpClient;
   private final ScheduledExecutorService executor;
   private final CompletableFuture<Void> started = new CompletableFuture<>();
+  private final CompletableFuture<Void> used = new CompletableFuture<>();
   /* Visible for testing. */ final AtomicBoolean sleeping = new AtomicBoolean();
   private final AtomicBoolean closing = new AtomicBoolean();
 
@@ -70,14 +71,21 @@ class OAuth2Client implements OAuth2Authenticator, Closeable {
             .getExecutor()
             .orElseGet(
                 () -> new OAuth2TokenRefreshExecutor(config.getBackgroundThreadIdleTimeout()));
-    currentTokensStage = started.thenApplyAsync((v) -> fetchNewTokens(), this.executor);
+    // when user interaction is not required, token fetch can happen immediately upon start();
+    // otherwise, it will be deferred until authenticate() is called the first time.
+    CompletableFuture<?> ready =
+        config.getGrantType().requiresUserInteraction()
+            ? CompletableFuture.allOf(started, used)
+            : started;
+    currentTokensStage = ready.thenApplyAsync((v) -> fetchNewTokens(), executor);
     currentTokensStage
         .whenComplete((tokens, error) -> log(error))
         .whenComplete((tokens, error) -> maybeScheduleTokensRenewal(tokens));
   }
 
   @Override
   public AccessToken authenticate() {
+    used.complete(null);
     Instant now = config.getClock().get();
     lastAccess = now;
     if (sleeping.compareAndSet(true, false)) {