chore(auth): Move hosted UI sign in to use case

[mattcreaser]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:

• WebUi Sign In logic refactored into coroutine-based usecase
• Code coverage added

How did you test these changes?

• Tests should pass

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(storage): message, feat(auth): message, chore(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 92.85714% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.64%. Comparing base (d09047f) to head (73d8f99).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3242      +/-   ##
==========================================
+ Coverage   55.50%   55.64%   +0.13%     
==========================================
  Files        1078     1079       +1     
  Lines       31911    31858      -53     
  Branches     4757     4751       -6     
==========================================
+ Hits        17711    17726      +15     
+ Misses      12356    12278      -78     
- Partials     1844     1854      +10     

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