[PM-15990] fix(identity): preserve port in IdentityServer Origin URL

[xinghejd]

🎟️ Tracking

https://github.com/bitwarden/server/issues/4981

📔 Objective

Previously, when using a custom port in self-hosted deployments (e.g., https://bitwarden.myserver.com:8443), the port information was lost during redirects from /identity/connect/authorize to /identity/sso/Login, despite having correctly configured globalSettings__baseServiceUri__vault.

This fix replaces Uri.Host with Uri.Authority when setting IdentityServer's Origin URL, ensuring:

• Port information is preserved in redirect URLs
• Maintains compatibility with both standard (443) and custom port deployments

📸 Screenshots

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[bitwarden-bot]

Thank you for your contribution! We've added this to our internal Community PR board for review. ID: PM-15990 Link: https://bitwarden.atlassian.net/browse/PM-15990

Details on our contribution process can be found here: https://contributing.bitwarden.com/contributing/pull-requests/community-pr-process.

[github-actions[bot]]

Checkmarx One – Scan Summary & Details – 031fefcc-1b4f-47a4-84d7-b25c9c68e5e5

Great job! No new security vulnerabilities introduced in this pull request

[codecov[bot]]

Codecov Report

:x: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 53.28%. Comparing base (480c20a) to head (3a3ce8c).

Files with missing lines	Patch %	Lines
bitwarden_license/src/Sso/Startup.cs	0.00%	1 Missing :warning:
src/Identity/Startup.cs	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5150      +/-   ##
==========================================
+ Coverage   53.26%   53.28%   +0.01%     
==========================================
  Files        1906     1906              
  Lines       84973    84973              
  Branches     7639     7639              
==========================================
+ Hits        45265    45275      +10     
+ Misses      37954    37944      -10     
  Partials     1754     1754              

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