> For the complete documentation index, see [llms.txt](https://k4k3ru.gitbook.io/k4k3ru-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://k4k3ru.gitbook.io/k4k3ru-docs/api/authentication/sign-request-with-go.md).

# Sign a Request with Go

Build an authenticated K4K3RU JSON-RPC request with Go. This example supports both `hmac-sha256` and `ed25519` credentials using only the Go standard library.

## Prerequisites

* Go 1.20 or later.
* An API credential created with `hmac-sha256` or `ed25519`.
* `K4K3RU_API_KEY`, `K4K3RU_SECRET_KEY`, and `K4K3RU_SIGNATURE_ALGORITHM` set in your environment.

## Example

Save this program as `main.go`:

```go
package main

import (
	"bytes"
	"crypto/ed25519"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

type auth struct {
	APIKey    string `json:"apiKey"`
	Timestamp int64  `json:"timestamp"`
	Nonce     string `json:"nonce"`
	Signature string `json:"signature"`
}

type request struct {
	ID     string          `json:"id"`
	Method string          `json:"method"`
	Params json.RawMessage `json:"params"`
	Auth   auth            `json:"auth"`
}

func main() {
	if err := run(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
}

func run() error {
	apiKey := os.Getenv("K4K3RU_API_KEY")
	secretKey := os.Getenv("K4K3RU_SECRET_KEY")
	algorithm := os.Getenv("K4K3RU_SIGNATURE_ALGORITHM")
	if apiKey == "" || secretKey == "" || algorithm == "" {
		return errors.New("set K4K3RU_API_KEY, K4K3RU_SECRET_KEY, and K4K3RU_SIGNATURE_ALGORITHM")
	}

	const method = "PaymentOnchain.CreateIntent"
	params, err := canonicalJSON([]byte(`{"productName":"usdc-base-mainnet-1"}`))
	if err != nil {
		return err
	}
	timestamp := time.Now().Unix()
	nonce, err := newNonce()
	if err != nil {
		return err
	}
	payload := strings.Join([]string{
		method,
		strconv.FormatInt(timestamp, 10),
		nonce,
		string(params),
	}, "\n")

	secret, err := base64.RawURLEncoding.DecodeString(secretKey)
	if err != nil {
		return fmt.Errorf("decode secret key: %w", err)
	}
	signature, err := sign(algorithm, secret, []byte(payload))
	if err != nil {
		return err
	}

	body, err := json.MarshalIndent(request{
		ID:     "1",
		Method: method,
		Params: params,
		Auth: auth{
			APIKey:    apiKey,
			Timestamp: timestamp,
			Nonce:     nonce,
			Signature: base64.RawURLEncoding.EncodeToString(signature),
		},
	}, "", "  ")
	if err != nil {
		return fmt.Errorf("encode request: %w", err)
	}
	fmt.Println(string(body))
	return nil
}

func canonicalJSON(raw []byte) ([]byte, error) {
	decoder := json.NewDecoder(bytes.NewReader(raw))
	decoder.UseNumber()
	var value any
	if err := decoder.Decode(&value); err != nil {
		return nil, fmt.Errorf("decode params: %w", err)
	}
	canonical, err := json.Marshal(value)
	if err != nil {
		return nil, fmt.Errorf("canonicalize params: %w", err)
	}
	return canonical, nil
}

func newNonce() (string, error) {
	value := make([]byte, 16)
	if _, err := rand.Read(value); err != nil {
		return "", fmt.Errorf("create nonce: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(value), nil
}

func sign(algorithm string, secret, payload []byte) ([]byte, error) {
	switch algorithm {
	case "hmac-sha256":
		mac := hmac.New(sha256.New, secret)
		if _, err := mac.Write(payload); err != nil {
			return nil, fmt.Errorf("sign payload: %w", err)
		}
		return mac.Sum(nil), nil
	case "ed25519":
		if len(secret) != ed25519.PrivateKeySize {
			return nil, fmt.Errorf("invalid Ed25519 private key length: %d", len(secret))
		}
		return ed25519.Sign(ed25519.PrivateKey(secret), payload), nil
	default:
		return nil, fmt.Errorf("unsupported signature algorithm: %s", algorithm)
	}
}
```

Run it with:

```bash
go run main.go
```

The program prints a request body that you can send to `https://api.k4k3ru.com/` with `Content-Type: application/json`. Replace the example product name with an active name returned by `AccountApp.ListProducts` before creating a real payment intent.

## Next Steps

See [API Request Authentication](/k4k3ru-docs/api/authentication.md) for canonicalization, freshness, replay-protection, and troubleshooting requirements.


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