feat(ui): SignIn code missing from yesterday

[joe-bell]

Description

Originally intended to be part of #3595, but lost in a dodgy rebase (see the original PR for further details and screenshots)

Additionally fixes SDKI-78

Checklist

• [x] npm test runs as expected.
• [x] npm run build runs as expected.
• [ ] (If applicable) JSDoc comments have been added or updated for any package exports
• [ ] (If applicable) Documentation has been updated

Type of change

• [ ] 🐛 Bug fix
• [x] 🌟 New feature
• [ ] 🔨 Breaking change
• [ ] 📖 Refactoring / dependency upgrade / documentation
• [ ] other:

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: c137b56314b1fec25fb2b86bbc9df75a4921abc9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 0 packages

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[joe-bell]

Additionally fixes SDKI-78 as part of this PR