8.5.14: Improved OAuth flow, enhanced signature verification, security fixes

[sosnovsky]

This PR updates version to 8.5.14 and adds changelog

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Tests (delete all except exactly one):

• Does not need tests (refactor only, docs or internal changes)

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[martgil]

LGTM! 👍

[martgil]

I had to rerun the tests, for the fragile test to pass.