deps: pin oauthlib>=4.0.0 (CVE-2026-49264, CVE-2026-49265)

[friedrichwilken]

Fixes #2720.

Two CVEs affect oauthlib 3.x:

• CVE-2026-49265 -- Timing attack in PKCE code_verifier comparison (CWE-208)
• CVE-2026-49264 -- Unsafe JSONP callback injection in RevocationEndpoint

The chain is kubernetes → requests-oauthlib → oauthlib>=3.0.0. Since requests-oauthlib only requires >=3.0.0, resolvers can land on the vulnerable 3.x line without a tighter constraint here.

The upstream fix is requests/requests-oauthlib#577 (bump their own lower bound to >=4.0.0), but that project is slow-moving. This PR adds the same protective direct pin used in #2016, following the same pattern that #2434 later cleaned up once the underlying issue was resolved.

The pin can be removed once requests-oauthlib ships a release with oauthlib>=4.0.0 in its own requirements.

[kubernetes-prow]

Welcome @friedrichwilken!

It looks like this is your first PR to kubernetes-client/python 🎉. Please refer to our pull request process documentation to help your PR have a smooth ride to approval.

You will be prompted by a bot to use commands during the review process. Do not be afraid to follow the prompts! It is okay to experiment. Here is the bot commands documentation.

You can also check if kubernetes-client/python has its own contribution guidelines.

You may want to refer to our testing guide if you run into trouble with your tests not passing.

If you are having difficulty getting your pull request seen, please follow the recommended escalation practices. Also, for tips and tricks in the contribution process you may want to read the Kubernetes contributor cheat sheet. We want to make sure your contribution gets all the attention it needs!

Thank you, and welcome to Kubernetes. 😃

[yliaog]

/lgtm
/approve
/release-note-none

[kubernetes-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: friedrichwilken, yliaog

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Details

Needs approval from an approver in each of these files:

• OWNERS [yliaog]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment