OAuth: Apache OLTU to Nimbusds

[ericenns]

Description of changes

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Related issue

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Checklist

Things for the developer to confirm they've done before the PR should be accepted:

• [ ] CHANGELOG.md (and UPGRADING.md if necessary) updated with information for new change.
• [ ] Tests added (or description of how to test) for any new features.
• [ ] User documentation updated for UI or technical changes.