[Authorization] Return if namespace policies are read only

[michaeljmarshall]

Motivation

This is a minor fix to a flow control in the default PulsarAuthorizationProvider class. Currently, when the policies are "read only", the grantPermissionAsync method will complete the future with a failure but then proceed to attempt to update the policy anyway.

Modifications

• Return from the method early when policies are marked as read only.

Verifying this change

This section of the code does not have good test coverage, so it wouldn't be very easy to add a test for this small case. Since this fix is small and easy to understand, I think it is safe to merge it without adding a test. Ideally, we'll come back and add tests for this part of the code base.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no
• The default values of configurations: no
• The wire protocol: no
• The rest endpoints: no
• The admin cli options: no
• Anything that affects deployment: no

Documentation

Check the box below and label this PR (if you have committer privilege).

Need to update docs?

• no-need-doc

It is a small change to internal behavior.

[michaeljmarshall]

@rdhabalia, @lhotari, @merlimat - PTAL

[michaeljmarshall]

/pulsarbot run-failure-checks

[github-actions]

@michaeljmarshall:Thanks for your contribution. For this PR, do we need to update docs?
(The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[michaeljmarshall]

@merlimat - given our discussion on #12515, I am going to close this PR and follow up with a new one that is asynchronous. It will solve the underlying issue for this PR and make the grantPermissionAsync method truly asynchronous.

[michaeljmarshall]

In order to cherry-pick this commit to older branches without also affecting the asynchronous code, I am going to re-open this PR. I'll submit a follow up that will make this method actually async.

[eolivelli]

Why dis you add the 'cherry picked' labels?
Did you cherry pick this change or are you planning to do so?

[michaeljmarshall]

@eolivelli - thanks for your question. I meant to put release labels, but instead used the cherry-picked label. I fixed it now. I'll merge this when tests pass and then I'll cherry pick to the old branches.