[PM-33508] feat: Add AuthenticatedBillingApi and BillingService network layer

[SaintPatrck]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-33508

📔 Objective

Add the billing network layer for premium upgrade and subscription management flows.

New files:

• AuthenticatedBillingApi — Retrofit interface with two endpoints:
  • POST /account/billing/vnext/premium/checkout (checkout session for free users upgrading)
  • POST /account/billing/vnext/portal-session (portal session for premium users managing subscription)
• CheckoutSessionRequestJson / CheckoutSessionResponseJson — request/response models for checkout
• PortalUrlResponseJson — response model for portal session
• BillingService / BillingServiceImpl — service interface and implementation wrapping the API; platform is hardcoded to "android" in the service layer

Modified files:

• BitwardenServiceClient / BitwardenServiceClientImpl — wire BillingService into the service client

Tests:

• BillingServiceTest — success and failure paths for both endpoints

[claude]

Claude finished @SaintPatrck's task in 2m 17s —— View job

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• Gather context and read changed files
• Perform code review
• Post review findings

Overall Assessment: APPROVE

This PR adds the AuthenticatedBillingApi, BillingService/BillingServiceImpl, and associated request/response models for the premium checkout and portal session endpoints. The implementation follows established service patterns in the network module, with proper NetworkResult to Result conversion and interface-based design. Test coverage includes success and failure cases for both endpoints using BaseServiceTest with MockWebServer.

Code Review Details

No findings identified. The code follows existing conventions for API definitions, service wrappers, serialization models, and test patterns.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.39%. Comparing base (453fc22) to head (b1a6ab0).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6668      +/-   ##
==========================================
+ Coverage   85.72%   86.39%   +0.66%     
==========================================
  Files         847      791      -56     
  Lines       58833    56939    -1894     
  Branches     8361     8359       -2     
==========================================
- Hits        50437    49193    -1244     
+ Misses       5492     4829     -663     
- Partials     2904     2917      +13     

Flag	Coverage Δ
app-data	17.67% <0.00%> (+0.21%)	⬆️
app-ui-auth-tools	20.80% <0.00%> (-0.27%)	⬇️
app-ui-platform	15.06% <0.00%> (-0.10%)	⬇️
app-ui-vault	25.83% <0.00%> (-0.70%)	⬇️
authenticator	6.64% <0.00%> (+0.03%)	⬆️
lib-core-network-bridge	4.30% <100.00%> (+0.02%)	⬆️
lib-data-ui	0.96% <0.00%> (+<0.01%)	⬆️

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[claude]

Overall Assessment: APPROVE

Reviewed the new billing network layer: AuthenticatedBillingApi, request/response models (CheckoutSessionRequestJson, CheckoutSessionResponseJson, PortalUrlResponseJson), BillingService/BillingServiceImpl, wiring into BitwardenServiceClient, and BillingServiceTest.

Code Review Details

No findings. The implementation cleanly follows established patterns:

• API interface uses NetworkResult<T> return type with authenticatedApiRetrofit, consistent with other authenticated APIs
• Service converts to Result<T> via toResult(), matching the repository result pattern
• Lazy initialization in BitwardenServiceClientImpl follows existing service wiring
• internal visibility for API and implementation, public for service interface
• KDoc present on all public APIs
• Tests cover success and failure paths for both endpoints using BaseServiceTest and MockWebServer

[github-actions]

Checkmarx One – Scan Summary & Details – 5bcd3c58-42b7-44d9-8244-835003240854

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Fixed Issues (1)

Great job! The following issues were fixed in this Pull Request

Severity	Issue	Source File / Package
	Use_of_Hardcoded_Password	/app/src/test/kotlin/com/x8bit/bitwarden/ui/vault/feature/attachments/AttachmentsViewModelTest.kt: 487

[claude]

Overall Assessment: APPROVE

Re-reviewed incremental changes across 2 new commits since previous review: 8887374 (add returnUrl request body to portal session endpoint) and cd1756e (rename checkoutUrl to checkoutSessionUrl in CheckoutSessionResponseJson). Both commits address reviewer feedback and align with established codebase patterns. No findings.

[aj-rosado]

LGTM, just a small nitpick

[aj-rosado]

⛏️ We tend to have constant values after imports

[aj-rosado]

Thank you for moving the constant @SaintPatrck

[SaintPatrck]

Thanks @aj-rosado and @david-livefront