> ## Documentation Index
> Fetch the complete documentation index at: https://docs.kraken.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Logon

> Authenticate and establish a FIX session using HMAC SHA-256 signature-based authentication.

The Logon message is used to authenticate and establish a FIX session. It includes signature-based authentication using HMAC SHA-256.

<Tabs>
  <Tab title="FIX Specification">
    <ParamField path="header" type="" required>
      MsgType <code>A</code>
    </ParamField>

    <ParamField path="108 - HeartBtInt" type="integer" required>
      Note same value used by both sides.
    </ParamField>

    <ParamField path="141 - ResetSeqNumFlag" type="boolean">
      Indicates both sides of a FIX session should reset sequence numbers.
    </ParamField>

    <ParamField path="96 - RawData" type="string" required>
      Contains signature (see below for creating a signature).
    </ParamField>

    <ParamField path="554 - Password" type="string" required>
      Contains the API Key for the Customer user.
    </ParamField>

    <ParamField path="trailer" type="" required />
  </Tab>

  <Tab title="Example">
    **Logon Request:**

    ```text theme={null}
    8=FIX.4.4|9=143|35=A|34=1|49=CUSTOMER|52=20220915-18:29:58.756|56={{ Customer }}|95=44|96=ZduZiNxyxS7_4UPDesOryd9KVEecg9LAqqTRR79Pp20=|98=0|108=60|141=Y|554=PMsU9ypImeJ0ad9X39ngzPYRA|10=248|
    ```

    **Logon Response:**

    ```text theme={null}
    8=FIX.4.4|9=78|35=A|34=1|49={{ Customer }}|52=20220915-18:29:58.765|56=CUSTOMER|98=0|108=60|141=Y|10=255|
    ```
  </Tab>
</Tabs>

## Creating a Signature

The signature is created by concatenating:

* SendingTime (52) as a string
* ASCII 01 value
* SeqNum (34) as a string
* ASCII 01 value
* SenderCompID (49)
* ASCII 01 value
* TargetCompID (56)

This string is then signed using the HMAC SHA-256 Algorithm and the API Secret for the API Key.

### Sample Java Code

```java theme={null}
/**
 * Takes a Message, an apiKey and apiSecret and uses the HMAC-SHA256 algorithm to
 * sign a FIX message by appending the sending-time sequenceNumber, SenderCompID 
 * and TargetCompID with \u0001 separator and signing using the secret, putting it 
 * into the RawBytes in Base64 encoding.
 */
private static void signLogon(final Message message,
                              final SessionID sessionId,
                              final String apiKey,
                              final String apiSecret) throws FieldNotFound {
    final var senderCompId = sessionId.getSenderCompID();
    final var targetCompId = sessionId.getTargetCompID();
    final var sendingTime = message.getString(SendingTime.FIELD);
    final var seqNum = message.getInt(MsgSeqNum.FIELD);
    final var sep = "\u0001";
    
    final var hmac = sign(apiSecret, sendingTime + sep + seqNum + sep + 
                         senderCompId + sep + targetCompId);
    
    message.setString(Password.FIELD, apiKey);
    message.setInt(RawDataLength.FIELD, hmac.length());
    message.setString(RawData.FIELD, hmac);
}

private static String sign(final String apiSecret, final String data) {
    final var mac = HmacUtils.getInitializedMac(HmacAlgorithms.HMAC_SHA_256,
                                               apiSecret.getBytes());
    final var encodedBytes = mac.doFinal(data.getBytes());
    final var encoder = Base64.getUrlEncoder(); //URL Safe Base64
    return encoder.encodeToString(encodedBytes);
}
```

<Note>
  **Dependencies**

  This sample relies on Apache Commons-Codec and QuickFIX for Java.
</Note>