Integrate Hanko with a Go backend

// SessionValidator defines the interface for session validation
type SessionValidator interface {
	ValidateSession(token string) (bool, error)
}

// HankoSessionValidator implements SessionValidator
type HankoSessionValidator struct {
	apiURL string
}

// ValidationResponse represents the Hanko API response
type ValidationResponse struct {
	IsValid bool `json:"is_valid"`
}

func NewHankoSessionValidator(apiURL string) *HankoSessionValidator {
	return &HankoSessionValidator{apiURL: apiURL}
}

func (v *HankoSessionValidator) ValidateSession(token string) (bool, error) {
	payload := strings.NewReader(fmt.Sprintf(`{"session_token":"%s"}`, token))

	req, err := http.NewRequest(http.MethodPost, v.apiURL+"/sessions/validate", payload)
	if err != nil {
		return false, fmt.Errorf("Failed to create request: %w", err)
	}

	req.Header.Add("Content-Type", "application/json")

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		return false, fmt.Errorf("Failed to send request: %w", err)
	}
	defer res.Body.Close()

	body, err := io.ReadAll(res.Body)
	if err != nil {
		return false, fmt.Errorf("Failed to read response: %w", err)
	}

	var validationRes ValidationResponse
	if err := json.Unmarshal(body, &validationRes); err != nil {
		return false, fmt.Errorf("Failed to parse response: %w", err)
	}

	return validationRes.IsValid, nil
}

func AuthMiddleware(validator SessionValidator) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			// Extract session token from cookie
			cookie, err := r.Cookie("hanko")
			if err != nil {
				http.Error(w, "Unauthorized", http.StatusUnauthorized)
				return
			}

			// Validate the session token
			isValid, err := validator.ValidateSession(cookie.Value)
			if err != nil {
				http.Error(w, "Internal Server Error", http.StatusInternalServerError)
				return
			}

			if !isValid {
				http.Error(w, "Unauthorized", http.StatusUnauthorized)
				return
			}

			// Continue to the next handler
			next.ServeHTTP(w, r)
		})
	}
}

// Usage example
func main() {
	validator := NewHankoSessionValidator("https://your-hanko-api-url.hanko.io")
	
	mux := http.NewServeMux()
	mux.HandleFunc("/protected", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("This is a protected endpoint!"))
	})

	// Apply authentication middleware to protected routes
	http.ListenAndServe(":8080", AuthMiddleware(validator)(mux))
}