> 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-rust.md).

# Sign a Request with Rust

Build an authenticated K4K3RU JSON-RPC request with Rust. This example supports both `hmac-sha256` and `ed25519` credentials.

## Prerequisites

* A current stable Rust toolchain.
* An API credential created with `hmac-sha256` or `ed25519`.
* `K4K3RU_API_KEY`, `K4K3RU_SECRET_KEY`, and `K4K3RU_SIGNATURE_ALGORITHM` set in your environment.

Create a project and add the example dependencies:

```bash
cargo new k4k3ru-signing
cd k4k3ru-signing
cargo add base64 ed25519-dalek hmac rand serde_json sha2
```

## Example

Replace `src/main.rs` with:

```rust
use base64::{engine::general_purpose::URL_SAFE_NO_PAD, Engine as _};
use ed25519_dalek::{Signer, SigningKey};
use hmac::{Hmac, Mac};
use rand::RngCore;
use serde_json::{json, Map, Value};
use sha2::Sha256;
use std::{env, error::Error, time::{SystemTime, UNIX_EPOCH}};

fn canonicalize(value: Value) -> Value {
    match value {
        Value::Array(values) => Value::Array(values.into_iter().map(canonicalize).collect()),
        Value::Object(values) => {
            let mut entries: Vec<_> = values.into_iter().collect();
            entries.sort_by(|left, right| left.0.cmp(&right.0));
            let mut sorted = Map::new();
            for (key, value) in entries {
                sorted.insert(key, canonicalize(value));
            }
            Value::Object(sorted)
        }
        other => other,
    }
}

fn sign(algorithm: &str, secret: &[u8], payload: &[u8]) -> Result<Vec<u8>, Box<dyn Error>> {
    match algorithm {
        "hmac-sha256" => {
            let mut mac = Hmac::<Sha256>::new_from_slice(secret)?;
            mac.update(payload);
            Ok(mac.finalize().into_bytes().to_vec())
        }
        "ed25519" => {
            if secret.len() != 64 {
                return Err(format!("invalid Ed25519 private key length: {}", secret.len()).into());
            }
            let seed: [u8; 32] = secret[..32].try_into()?;
            Ok(SigningKey::from_bytes(&seed).sign(payload).to_bytes().to_vec())
        }
        _ => Err(format!("unsupported signature algorithm: {algorithm}").into()),
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let api_key = env::var("K4K3RU_API_KEY")?;
    let secret = URL_SAFE_NO_PAD.decode(env::var("K4K3RU_SECRET_KEY")?)?;
    let algorithm = env::var("K4K3RU_SIGNATURE_ALGORITHM")?;
    let method = "PaymentOnchain.CreateIntent";
    let params = json!({"productName": "usdc-base-mainnet-1"});
    let canonical_params = serde_json::to_string(&canonicalize(params.clone()))?;
    let timestamp = SystemTime::now().duration_since(UNIX_EPOCH)?.as_secs();
    let mut nonce_bytes = [0_u8; 16];
    rand::thread_rng().fill_bytes(&mut nonce_bytes);
    let nonce = URL_SAFE_NO_PAD.encode(nonce_bytes);
    let payload = format!("{method}\n{timestamp}\n{nonce}\n{canonical_params}");
    let signature = URL_SAFE_NO_PAD.encode(sign(&algorithm, &secret, payload.as_bytes())?);

    let request = json!({
        "id": "1",
        "method": method,
        "params": params,
        "auth": {
            "apiKey": api_key,
            "timestamp": timestamp,
            "nonce": nonce,
            "signature": signature
        }
    });
    println!("{}", serde_json::to_string_pretty(&request)?);
    Ok(())
}
```

Run it with:

```bash
cargo run
```

The program prints a request body that you can send to `https://api.k4k3ru.com/` with `Content-Type: application/json`. Build the canonical payload and request from the same `params` value.

## Next Steps

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


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