fix: check credential expiration timestamp when generating tokens

[lyoung-confluent]

What this PR does / why we need it:

There are two expirations which must be considered when using a signed EKS token:

• 15 minutes after the point in time when the AWS STS request has been signed
• The underlying AWS credentials can expire at which point the token won't be accepted

The second case is particularly common when making frequent requests while using AssumeRole or AssumeRoleWithWebRequest as mentioned in #590 as the default session timeout is 1 hour.

This PR adds an additional check fetching the AWS credential expiration and using that as the returned expiration if it is before the 15 minute token expiration.

Which issue(s) this PR fixes

• Fixes #590

[linux-foundation-easycla[bot]]

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[k8s-ci-robot]

Hi @lyoung-confluent. Thanks for your PR.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: lyoung-confluent Once this PR has been reviewed and has the lgtm label, please assign micahhausler for approval. For more information see the Kubernetes Code Review Process.

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[alvaroaleman]

/ok-to-test

[micahhausler]

Sorry for the late review, and thank you! This looks like a worthwhile change. Would you mind adding test coverage and signing the CNCF CLA?

[alvaroaleman]

Taking this over in https://github.com/kubernetes-sigs/aws-iam-authenticator/pull/737 as @lyoung-confluent is busy otherwise at the moment. /close

[k8s-ci-robot]

@alvaroaleman: Closed this PR.

In response to this:

Taking this over in https://github.com/kubernetes-sigs/aws-iam-authenticator/pull/737 as @lyoung-confluent is busy otherwise at the moment. /close

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