users: harden, test, and add cleaner of identifier

[kradalby]

Fixes #2584
Fixes #2474

[ghost]

Pull Request Revisions

Revision	Description
r2	Enhanced OIDC identifier generation and cleaning Improved Identifier() and CleanIdentifier() methods for better handling of whitespace, URL schemes, and path segments
r1	Improved OIDC identifier handling logic Added robust identifier cleaning and generation methods for OIDC claims, including handling URLs, double slashes, and edge cases in provider identifiers

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✅ AI review completed for r2

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