[PM-30271] Create Retrieve Eligible Subscription Discounts Endpoint

[sbrown-livefront]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-30271

📔 Objective

This pull request introduces a new API endpoint for retrieving eligible subscription discounts for a user and implements the supporting backend infrastructure for discount eligibility evaluation. It adds new service interfaces, implementations, audience filter logic, and comprehensive tests to ensure correct discount selection and mapping.

API and Controller Enhancements:

• Added a new GET /discounts endpoint in AccountBillingVNextController that returns all applicable subscription discounts for the authenticated user. This endpoint is feature-flagged and uses a new query interface to fetch eligible discounts.

Discount Eligibility Infrastructure:

• Introduced the ISubscriptionDiscountService interface and its implementation SubscriptionDiscountService to manage discount eligibility checks, including support for audience-based rules.
• Added the IDiscountAudienceFilter interface and a factory (IDiscountAudienceFilterFactory/DiscountAudienceFilterFactory) for returning DI filters based on discount targeting rules, with an initial implementations for "UserHasNoPreviousSubscriptions" and "AllUsers".

Query and Response Models:

• Created the IGetApplicableDiscountsQuery interface and its implementation to return eligible discounts mapped to the new SubscriptionDiscountResponseModel, which includes all relevant discount details.

Dependency Injection and Service Registration:

• Registered all new services, queries, and filter factories in the payment service registration module to ensure proper DI resolution.

Stripe Integration and Constants

• Expanded StripeConstants to include product IDs and a utility to map Stripe product IDs to discount tiers, and added a method to list subscriptions via Stripe.

API Response Model

• Added SubscriptionDiscountResponseModel to standardize the API response for discount information, including per-tier eligibility.

Note: Stripe Product IDs are no longer returned with discounts

📸 Screenshots

Screen.Recording.2026-03-03.at.10.51.35.AM.mov

[github-actions]

Checkmarx One – Scan Summary & Details – dbc85790-8a12-4c53-8d04-56beb7b51734

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

[codecov]

Codecov Report

❌ Patch coverage is 95.60440% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.52%. Comparing base (cc12c72) to head (8702e47).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...nceFilters/UserHasNoPreviousSubscriptionsFilter.cs	93.05%	3 Missing and 2 partials ⚠️
...ces/Implementations/SubscriptionDiscountService.cs	93.75%	0 Missing and 2 partials ⚠️
.../Billing/Services/Implementations/StripeAdapter.cs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7063      +/-   ##
==========================================
+ Coverage   56.44%   56.52%   +0.07%     
==========================================
  Files        2013     2020       +7     
  Lines       88089    88270     +181     
  Branches     7855     7875      +20     
==========================================
+ Hits        49720    49892     +172     
- Misses      36554    36559       +5     
- Partials     1815     1819       +4     

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[kdenney]

Looking good and getting closer! 👏 A few notes and suggestions.

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[kdenney]

Looks good; nice job!