Comprehensive cleanup to use WriteSuccessResponse and WriteErrorResponse

[JeethJJ]

With [1] we have introduced WriteSuccessResponse and WriteErrorResponse helper methods. In this PR we are modifying all the places with references to use this newly introduced until methods.

[1] #845

Related Issues

• Cleanup api handler request handle implementation #442

[Copilot]

Pull request overview

This PR comprehensively refactors HTTP response handling across the backend to use the newly introduced WriteSuccessResponse and WriteErrorResponse utility methods from internal/system/utils. The changes eliminate code duplication, ensure consistent error handling and logging, and improve maintainability by centralizing JSON encoding logic.

Key Changes:

• Replaced manual JSON encoding and header setting with WriteSuccessResponse and WriteErrorResponse utilities across all handlers
• Removed redundant helper functions like buildUserSchemaResponse, writeToResponse, and handleEncodingError from individual packages
• Updated test expectations to check for the standard encoding error message from the utility functions
• Removed unused encoding/json imports where no longer needed

Reviewed changes

Copilot reviewed 23 out of 23 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
backend/internal/userschema/handler.go	Replaced manual JSON encoding with utility methods; removed buildUserSchemaResponse helper
backend/internal/user/handler.go	Converted all HTTP responses to use utility methods; improved error response consistency
backend/internal/system/healthcheck/handler/healthcheckhandler.go	Updated to use WriteSuccessResponse with conditional status codes
backend/internal/system/export/handler.go	Migrated to utility methods; contains minor formatting issue on line 54
backend/internal/role/handler.go	Removed writeToResponse and handleEncodingError helpers; migrated to utility methods
backend/internal/role/handler_test.go	Removed obsolete tests for deleted helper functions
backend/internal/oauth/oauth2/userinfo/handler.go	Simplified response handling while preserving OAuth2-specific headers
backend/internal/oauth/oauth2/token/token_handler.go	Cleaned up import organization and migrated to utility methods
backend/internal/oauth/oauth2/introspect/handler.go	Only success responses migrated; error responses use OAuth2-specific format
backend/internal/oauth/oauth2/discovery/handler.go	Added debug logging and migrated to utility methods
backend/internal/oauth/oauth2/dcr/handler.go	Removed unused logger variable; migrated to utility methods
backend/internal/oauth/oauth2/authz/handler.go	Fixed duplicate import; migrated to utility methods
backend/internal/oauth/jwks/handler.go	Migrated to utility methods for both success and error responses
backend/internal/notification/message_handler.go	Comprehensive migration to utility methods across all handlers
backend/internal/idp/handler.go	Migrated all CRUD operations to use utility methods
backend/internal/group/handler.go	Migrated to utility methods across all handlers
backend/internal/group/handler_test.go	Updated test expectations for encoding error messages
backend/internal/flow/flowexec/handler.go	Migrated to utility methods with improved status code handling
backend/internal/branding/handler.go	Removed helper functions; migrated to utility methods
backend/internal/branding/handler_test.go	Removed tests for deleted helper functions
backend/internal/authn/handler.go	Removed custom response helper methods; migrated to utility methods
backend/internal/application/handler.go	Comprehensive migration to utility methods across all handlers

[codecov]

Codecov Report

❌ Patch coverage is 80.11696% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.62%. Comparing base (b406864) to head (2b862f3).
⚠️ Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
backend/internal/user/handler.go	30.76%	27 Missing ⚠️
backend/internal/system/export/handler.go	50.00%	5 Missing ⚠️
backend/internal/flow/flowexec/handler.go	80.00%	1 Missing ⚠️
backend/internal/userschema/handler.go	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #878      +/-   ##
==========================================
+ Coverage   87.22%   87.62%   +0.39%     
==========================================
  Files         302      310       +8     
  Lines       24017    23852     -165     
  Branches      606      606              
==========================================
- Hits        20949    20900      -49     
+ Misses       1886     1825      -61     
+ Partials     1182     1127      -55     

Flag	Coverage Δ
backend-integration-postgres	59.00% <56.72%> (+0.08%)	⬆️
backend-integration-sqlite	58.96% <56.72%> (+0.08%)	⬆️
backend-unit	73.59% <68.42%> (+0.32%)	⬆️
frontend-apps-develop-unit	88.45% <ø> (ø)

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