feat: honor KEY_PROVIDER_URL scheme and validate at config load

[danielpeng1]

Stop rewriting the key provider URL in the client and validate provider URLs at config load.

• KeyProviderClient: use the configured URL scheme; keep existing mTLS agent behavior when TLS_MODE=mtls
• initConfig: validate KEY_PROVIDER_URL and optional BACKUP_KMS_URL; add ALLOW_PLAINTEXT_KEY_PROVIDER for local/dev setups
• README and docker-compose.yml updates for the new env var

Tests

• config.test.ts: URL scheme validation
• keyProviderClient.test.ts: no scheme downgrade when TLS is disabled on the app

Ticket: WCN-1927

[linear-code]

WCN-1927

[danielpeng1]

@claude review

[github-actions]

Claude finished @danielpeng1's task —— View job

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PR Review: Key Provider URL Scheme Validation

Todo List:

• Read and analyze changed files
• Review configuration changes in initConfig.ts
• Review KeyProviderClient changes
• Analyze test coverage and quality
• Check documentation updates
• Provide comprehensive review feedback

Review Summary

This PR successfully implements URL scheme validation for key provider configurations and stops automatic URL rewriting in the client. The implementation is well-designed and addresses important security concerns around plaintext HTTP usage.

✅ Strengths

Security-Focused Design

• Explicit scheme validation: validateKeyProviderUrl() in initConfig.ts:139-164 properly validates URL schemes and rejects invalid configurations
• Safe defaults: Requires ALLOW_PLAINTEXT_KEY_PROVIDER=true for HTTP URLs, preventing accidental plaintext key transmission
• Clear security warnings: Logs prominent warnings when plaintext HTTP is used (lines 161-163)

Clean Client Implementation

• Honors configured scheme: KeyProviderClient in keyProviderClient.ts:40-55 now respects the configured URL scheme instead of rewriting it
• Preserved mTLS behavior: Agent configuration still works correctly when TLS_MODE=mtls (lines 43-53)
• Simplified logic: Removed complex URL rewriting, making the code more predictable

Comprehensive Test Coverage

• URL scheme validation tests: config.test.ts:319-377 covers all validation scenarios including edge cases
• Client behavior verification: keyProviderClient.test.ts:228-251 ensures no unwanted scheme downgrading
• Both positive and negative test cases: Proper error conditions and success scenarios

Good Documentation

• Updated README: Clear explanation of the new environment variable and security implications
• Docker compose example: Shows proper usage with the new flag for development

🔍 Code Quality Observations

Configuration Validation (initConfig.ts)

// Lines 139-164: Well-structured validation function
function validateKeyProviderUrl(url: string, envVar: string, tlsMode: TlsMode): void {
  // Good: Proper URL parsing with error handling
  // Good: Clear error messages with context
  // Good: Security-conscious defaults
}

Client Changes (keyProviderClient.ts)

// Lines 40-55: Simplified and more predictable
const urlObj = new URL(cfg.keyProviderUrl);
// Good: Honors the configured scheme
// Good: Only sets up agent when actually needed for mTLS

💡 Minor Suggestions

1. Error Message Consistency: The validation function could benefit from more consistent error message formatting across different validation failures.

2. Type Safety: Consider adding a branded type for validated URLs to prevent passing unvalidated URLs to the client.

✅ Test Quality

The test coverage is excellent:

• Comprehensive validation scenarios: All URL scheme combinations tested
• Error message verification: Tests check specific error content
• Client behavior verification: Ensures no regression in URL handling
• Edge cases covered: Invalid URLs, missing schemes, backup KMS validation

📋 Final Assessment

Approve: This is a well-implemented security enhancement that:

• ✅ Properly validates URL schemes at config load time
• ✅ Maintains backward compatibility with existing configurations
• ✅ Provides clear security guidance through warnings and documentation
• ✅ Has comprehensive test coverage
• ✅ Simplifies client code by removing URL rewriting logic

The PR successfully addresses the ticket requirements (WCN-1927) and improves the security posture of the application by making URL scheme handling explicit and validated.

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Job Run: Link | Branch: WCN-1927/key-provider-url-scheme