Make AuthProvider.content() return CompletableFuture for async auth flows

[ricardozanini]

Current API

public interface AuthProvider {
  String scheme();
  String content(WorkflowContext workflow, TaskContext task, WorkflowModel model, URI uri);
}

Problem

The content() method returns String synchronously, forcing implementers to block on async operations.

For OAuth2/OIDC flows using reactive clients (e.g., Quarkus OIDC Client with Uni<Tokens>), we must block:

@Override
public String content(...) {
    // Quarkus OIDC Client returns Uni<Tokens> (async)
    Uni<Tokens> tokensUni = client.getTokens();
    
    // FORCED TO BLOCK - wasteful! 🚫
    Tokens tokens = tokensUni.await().atMost(connectionTimeout);
    return tokens.getAccessToken();
}

This wastes threads and prevents efficient reactive pipelines.

Proposed API

public interface AuthProvider {
  String scheme();
  CompletableFuture<String> content(WorkflowContext workflow, TaskContext task, WorkflowModel model, URI uri);
}

Benefits

• ✅ Non-blocking: Reactive auth clients can chain naturally
• ✅ Thread efficiency: No blocking during token negotiation
• ✅ Backward compatible: Existing sync implementations return CompletableFuture.completedFuture(value)

Example: Async OAuth2 Implementation

@Override
public CompletableFuture<String> content(...) {
    return client.getTokens()                    // Uni<Tokens>
        .convert().toCompletionStage()           // CompletionStage<Tokens>
        .toCompletableFuture()                   // CompletableFuture<Tokens>
        .thenApply(Tokens::getAccessToken);      // CompletableFuture<String>
}

Migration for Existing Implementations

Sync implementations wrap with completedFuture:

@Override
public CompletableFuture<String> content(...) {
    String token = /* compute synchronously */;
    return CompletableFuture.completedFuture(token);
}

---

Impact: Low - small API change, high performance benefit for reactive auth flows.

[matheusandre1]

free pr master?

[ricardozanini]

free pr master?

I think @fjtirado will take this one.