allow to return jag token with subset of scopes

[havetisyan]

Description

since the mcp client might ask for multiple roles, there is no need to reject the jag issue token if the user only has a subset of role access. instead we'll just return the subset. #3100

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.

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[gemini-code-assist]

Summary of Changes

Hello @havetisyan, 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 refines the ZTS service's handling of JAG token requests. It transitions from an "all-or-nothing" approach for role access to a more flexible model where a token is issued with a subset of requested roles if the user lacks full access. This change prevents unnecessary rejections for clients like MCP that might request multiple roles, ensuring a token is still provided for the accessible permissions.

Highlights

• JAG Token Issuance Logic: The logic for issuing JAG tokens has been updated. Previously, a request for multiple roles would fail if the user didn't have access to all requested roles. Now, the system will issue a token containing only the subset of roles the user does have access to, as long as at least one role is granted.
• Test Case Adjustment: The testProcessAccessTokenJAGExchangePartialAccess test case was modified to reflect the new behavior. It now verifies that a token with partial scopes is successfully returned, rather than asserting a FORBIDDEN exception.

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[gemini-code-assist]

Code Review

This pull request modifies the behavior of JAG token issuance to allow returning a subset of requested scopes if the user has partial access, instead of rejecting the request. The change in ZTSImpl.java correctly implements this new logic by checking if the set of accessible roles is empty, rather than comparing its size with the number of requested roles. The corresponding test case in ZTSImplAccessTokenTest.java has been updated to validate this new behavior. The changes look good and align with the stated goal. I've added one suggestion to improve the test assertion's robustness.

[yosrixp]

Looks good