A production-ready HTTP client package with automatic token management, caching, and retry logic for service-to-service communication

The new pkg/http package provides:

• Automatic Token Management: Fetches and caches service tokens with expiration handling
• Token Refresh on 401: Automatically refreshes tokens when receiving 401 Unauthorized responses
• Retry Logic: Configurable retry with exponential backoff for failed requests
• Thread-Safe: Safe for concurrent use with proper locking
• Context Support: Full context.Context support for cancellation and timeouts
• Request/Response Hooks: Extensible hooks for custom request/response processing
• JSON Helpers: Convenient methods for JSON requests and responses

Key Features

• OAuth2 client credentials token provider implementation
• Static and custom token provider support
• Automatic token caching until expiration
• Automatic retry on 401 with token refresh
• Configurable retry attempts with exponential backoff
• Base URL support for API clients
• Request/response hooks for extensibility

Usage

provider := http.NewOAuth2ClientCredentialsProvider(
    "https://auth.example.com/oauth/token",
    "client-id",
    "client-secret",
    "read write",
)

client := http.NewClient(
    http.WithTokenProvider(provider, 30*time.Second),
    http.WithLogger(logger),
    http.WithRetry(3, 100*time.Millisecond),
    http.WithBaseURL("https://api.example.com"),
)

resp, err := client.Get(ctx, "/api/v1/users")