config: support environment variable macros in apiKeys

[mostlygeek]

Summary

• Add ${env.VAR_NAME} macro support for apiKeys configuration field
• Apply env macro substitution before validation checks
• Add tests for env macro substitution in apiKeys

Summary by CodeRabbit

• New Features

  • API keys now support environment variable substitution within configuration files.
  • Added validation to ensure API keys do not contain spaces following environment variable substitution.

• Tests

  • Added comprehensive test suite covering environment variable substitution in API keys, including error handling validation for missing variables and empty keys after substitution.

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[coderabbitai]

Walkthrough

The PR extends config loading to substitute environment variable macros in API keys during validation. The implementation adds macro expansion logic to each API key prior to validation, checks for spaces in substituted keys, and includes comprehensive test coverage for successful and failed substitutions.

Changes

Cohort / File(s)	Summary
API Key Environment Variable Substitution proxy/config/config.go, proxy/config/config_test.go	Modified LoadConfigFromReader to substitute environment variable macros in API keys before validation; added loop with index-based key updates, space validation, and error handling. Added comprehensive test suite TestConfig_APIKeys_EnvMacros with four subtests covering successful single/multiple substitutions, missing variable error propagation, and empty key validation.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• Feature request: Support environment variable expansion for apiKeys #462: Directly addresses the feature implemented here—environment variable substitution for API keys during config loading with proper error handling and validation.

Possibly related PRs

• config: add environment variable macros #466: Also implements environment-variable macro substitution in config loading for similar functionality.
• Add macros to Configuration schema #149: Extends LoadConfigFromReader with substitution logic, though for user-defined macros in model fields rather than environment variables in API keys.

Suggested labels

enhancement, configuration

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding environment variable macro support for apiKeys configuration.

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✨ Finishing touches

• 📝 Generate docstrings

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[mostlygeek]

Well the one reason to do #466 was not done 🤣 . At least I tested it.