Minimal Go backend with Clerk authentication

main.go

package main

import (
	"context"
	"fmt"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/clerk/clerk-sdk-go/v2"
	clerkhttp "github.com/clerk/clerk-sdk-go/v2/http"
	"github.com/joho/godotenv"
	"github.com/labstack/echo/v4"
	"github.com/labstack/echo/v4/middleware"
	"github.com/labstack/gommon/log"
)

// ClerkMiddleware creates a middleware for Echo that handles Clerk authentication
func ClerkMiddleware(next echo.HandlerFunc) echo.HandlerFunc {
	return func(c echo.Context) error {
		// Use the Clerk SDK's middleware function under the hood
		handler := clerkhttp.WithHeaderAuthorization()(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Update Echo's context with the modified request context from Clerk
			c.SetRequest(r)
			// Continue processing the request
			next(c)
		}))

		// Call the Clerk middleware handler
		handler.ServeHTTP(c.Response().Writer, c.Request())

		// The status code is already written by the Clerk middleware if there was an error
		// So we only return nil to prevent Echo from trying to write a response again
		return nil
	}
}

func main() {
	// Load environment variables from .env file
	if err := godotenv.Load(); err != nil {
		log.Warn("No .env file found")
	}

	// Initialize Clerk with API key from environment variable
	clerkAPIKey := os.Getenv("CLERK_API_KEY")
	if clerkAPIKey == "" {
		log.Fatal("CLERK_API_KEY environment variable is required")
	}
	clerk.SetKey(clerkAPIKey)

	// Create a new Echo instance
	e := echo.New()
	e.Logger.SetLevel(log.INFO)

	// Add middleware
	e.Use(middleware.Logger())
	e.Use(middleware.Recover())
	e.Use(middleware.CORS())

	// Public routes
	e.GET("/", func(c echo.Context) error {
		return c.JSON(http.StatusOK, map[string]string{
			"access": "public",
		})
	})

	// Protected routes
	api := e.Group("/api")
	api.Use(ClerkMiddleware)

	api.GET("", func(c echo.Context) error {
		// Get the session claims from the context using the Clerk SDK helper
		claims, ok := clerk.SessionClaimsFromContext(c.Request().Context())
		if !ok {
			return c.JSON(http.StatusUnauthorized, map[string]string{
				"access": "unauthorized",
			})
		}
		return c.JSON(http.StatusOK, map[string]string{
			"user_id": claims.Subject,
		})
	})

	api.GET("/user/profile", getUserProfile)

	e.GET("/health", healthCheck)

	// Start server
	serverPort := os.Getenv("SERVER_PORT")
	if serverPort == "" {
		serverPort = "3000"
	}

	// Start server in a goroutine so it doesn't block
	go func() {
		if err := e.Start(fmt.Sprintf(":%s", serverPort)); err != nil && err != http.ErrServerClosed {
			e.Logger.Fatal("shutting down the server")
		}
	}()

	// Wait for interrupt signal to gracefully shutdown the server
	quit := make(chan os.Signal, 1)
	signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
	<-quit

	// Graceful shutdown
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	if err := e.Shutdown(ctx); err != nil {
		e.Logger.Fatal(err)
	}
}

// Health check handler
func healthCheck(c echo.Context) error {
	return c.JSON(http.StatusOK, map[string]string{
		"status": "healthy",
	})
}

// Get user profile handler
func getUserProfile(c echo.Context) error {

	claims, ok := clerk.SessionClaimsFromContext(c.Request().Context())
	if !ok {
		return c.JSON(http.StatusUnauthorized, map[string]string{
			"access": "unauthorized",
		})
	}

	// Build profile data
	profile := map[string]interface{}{
		"id": claims.ID,
	}

	return c.JSON(http.StatusOK, profile)
}