Allow wrapper-controlled init to fix jwk_uri backward compatibility (Issue #3054)

[sh1myama]

Description

Context

• In v1.12.x, jwk_uri became mandatory and the check runs in a static initializer, which prevents wrappers from setting system properties before AuthZpeClient loads. (Issue jwk_uri property is now mandatory in v1.12.1, breaking backward compatibility #3054)

Changes

• Move access-token resolver setup out of the static initializer into AuthZpeClient.init() so callers can set properties before initialization.
• Keep the existing jwk_uri requirement for access-token validation, but make its initialization explicit and controllable.
• Add support for an optional athenz.zpe.jwk_proxy_uri and pass it into setAccessTokenSignKeyResolver to enable proxied JWK fetches.

Outcome

• Restores upgrade path for Role Token users by avoiding premature jwk_uri validation during class load, while preserving access-token behavior when init() is called.

Contribution Checklist:

• The pull request does not introduce any breaking changes
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

Attach Screenshots (Optional)

[gemini-code-assist]

Summary of Changes

Hello @sh1myama, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical backward compatibility issue where the jwk_uri validation was prematurely triggered during class loading, preventing applications from properly initializing. By refactoring the initialization logic into an explicit method and introducing an optional proxy configuration, it restores the upgrade path for Role Token users and enhances flexibility for JWK fetching, ensuring a smoother integration and operation of the Athenz ZPE client.

Highlights

• Wrapper-Controlled Initialization: The setup for the access-token resolver has been moved out of the static initializer into the AuthZpeClient.init() method. This allows external wrappers to set system properties before the AuthZpeClient loads, resolving a backward compatibility issue with jwk_uri.
• Explicit JWK URI Validation: The requirement for jwk_uri remains for access-token validation, but its initialization is now explicit and controllable, preventing premature validation during class loading.
• JWK Proxy Support: Added support for an optional athenz.zpe.jwk_proxy_uri system property, which is passed into setAccessTokenSignKeyResolver to enable proxied JWK fetches.

Changelog

• clients/java/zpe/src/main/java/com/yahoo/athenz/zpe/AuthZpeClient.java
  • Moved the access token signing key resolver initialization from the static block to the init() method.
  • Modified the initializeAccessTokenSignKeyResolver() method to retrieve an optional jwk_proxy_uri system property.
  • Updated the setAccessTokenSignKeyResolver method call to include the new proxyUrl parameter.
• clients/java/zpe/src/main/java/com/yahoo/athenz/zpe/ZpeConsts.java
  • Added a new constant ZPE_PROP_JWK_PROXY_URI for the athenz.zpe.jwk_proxy_uri system property.

Activity

• No human activity has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request refactors the initialization logic in AuthZpeClient by moving the access token resolver setup to an explicit init() method, which resolves issues with jwk_uri system properties and introduces support for a JWK proxy URI. However, a high-severity Server-Side Request Forgery (SSRF) vulnerability has been identified due to a lack of URL validation for the new JWK proxy URI feature; implementing a strict allow-list for proxy servers is recommended. Furthermore, the new init() method has a potential thread-safety issue and should be made idempotent to prevent race conditions during concurrent initialization.

[gemini-code-assist]

The new init() method is not thread-safe or idempotent. If called concurrently (e.g., during application startup or in parallel tests), it can lead to race conditions during the initialization of static resources. It's a best practice to ensure that initialization methods like this execute only once.

You can make this method thread-safe and idempotent by using a static flag with double-checked locking. This will ensure the initialization logic is performed safely and exactly one time.

Example:

// Add this field to the class
private static volatile boolean zpeInitialized = false;

// Modify the init() method
public static void init() {
    // Quick check without lock
    if (zpeInitialized) {
        return;
    }
    synchronized (AuthZpeClient.class) {
        // Check again inside the synchronized block
        if (zpeInitialized) {
            return;
        }

        if (LOG.isDebugEnabled()) {
            LOG.debug("Init: load the ZPE");
        }

        // ... current init logic ...
        initializeAccessTokenSignKeyResolver();
        // ... other set calls that were moved ...

        zpeInitialized = true;
    }
}

[havetisyan]

@sh1myama the AuthZpeClient.init() was never required for ZPE functionality. So by moving the actual keyresolver initialization into that function will break most zpe users, so not the correct solution.

I'll check in the next couple of days in more detail and will propose how to address your use case.

[sh1myama]

@havetisyan -san

@sh1myama the AuthZpeClient.init() was never required for ZPE functionality. So by moving the actual keyresolver initialization into that function will break most zpe users, so not the correct solution.

I'll check in the next couple of days in more detail and will propose how to address your use case.

Thank you for checking.

In the following Java decentralized access control sample, the documentation says to initialize the ZPE Client in init when performing authorization checks, so I understood that calling init is mandatory.
https://github.com/AthenZ/athenz/blob/master/docs/example_java_decentralized_access.md#authorization-checks

Even if we apply this change and modify it so that initializeAccessTokenSignKeyResolver is called from init, my understanding is that the behavior will not change as long as the implementation is written to always call init itself.

Thank you in advance.

[havetisyan]

@sh1myama here is what changes we need to make:

1. introduce a static variable tokenSignKeyResolverInitialized that key resolver is initialized with default value false
2. update the initializeAccessTokenSignKeyResolver to take a boolean argument whether or not return exceptions or just return without any errors.
3. in the static initializer call the method with false value. if the variables are not set, it will just return without any exceptions, otherwise it will set the initializer and set the tokenSignKeyResolverInitialized to true.
4. In the init function, introduce a new system property athenz.zpe.jwk_uri_required with a default value of true. If the value is false, then do nothing and return. If the value is true (default value), it will check the value for tokenSignKeyResolverInitialized. If it's false then it will call the initializeAccessTokenSignKeyResolver method with the true argument so that it will return an exception if there are any errors (current behavior).

this would allow your applications to set the either set the jwks_uri to complete the sign key resolver or jwks_uri_required to false in your application and ignore calling the method completely.

[sh1myama]

@havetisyan -san
Sorry for the late reply. Thank you for your suggestion. I will review the content you provided.

[sh1myama]

@havetisyan -san
I have revised the code based on the advice you provided.
Since athenz.zpe.jwk_uri_required is not necessary in our environment, I have not added it.
Do you have any concerns about these changes?

[havetisyan]

let's move this setMillisBetweenZtsCalls as the last line in the initializeAccessTokenSignKeyResolver method. this way we don't have to repeat the call twice once here and then once again in init method