# Authentication

For app's server to request any data from the Fyre server using APIs, it needs to authentication itself to Fyre backend.

Authentication happens on every single request by sending a digital signature in the request body. The Fyre server verifies the signature before sending data.

In order to generate a signature, the app's server need to sign message (`message` feld of the request body) using registered app's private key and send the signature in `fyresign` field of the request body.

Sample code snippet to generate signature in Javascript:

```javascript
// Require web3 packages
const web3 = require("web3");
const Web3 = new web3();

// generates signature and messageHash
const generateSignature = async (privateKey, message) => {
const { signature, messageHash } = await Web3.eth.accounts.sign(
    JSON.stringify(message),
    privateKey
  );
  return {
    message,
    fyresign: signature,
    messageHash
  };
};
// sample request message 
const message = {
  "appId": "6274a30fc43e35144642a484",
  "externalUserId": "456fhrghtuht374",
  "eventId": "6274b4cde7556226721e620c",
  "isEmail": false,
  "iat": Math.floor(Date.now() / 1000); //in seconds,
  "exp": Math.floor((Date.now() + (3600 * 24 * 1000)) / 1000),  //valid for a day,
  "metaData": {
    "limit": 10, // fetching 10 records 
    "page": 1,
  }
}
const privateKey = "0x5b79b6758d25694e8fef4f769a48f768bf838dd17fec4d9c54bcf7cd3b4a0e1a"; // generated during app's registration on Hyperfyre admin dashboard.
const { message, fyresign, messageHash } = generateSignature(privateKey, message);
```

In the above code, we used standard `web3` package to generate digital signature. There are libraries available in various different languages like JavaScript, Go etc which can used based on requirement.

To sign a message, all you have to do is, use `web3.eth.sign()` function. The funcation takes two parameters:

* a `message`: Will contain the request parameters, depending on the need.
* a `privateKey`: Generated during the app registration phase.

`web3.eth.sign()` returns three values `message`, `signature` and `messageHash`.

The server need to send all these parameters in the request body of any API call to Fyre backend.

> **Note:**
>
> 1. Make sure to send the `signature` in the `fyresign` field in the request body.
> 2. We only accept message in specific format. Read the API documentation to understand the message format.

***

We learnt how an app's server can produce a digital signature in order to authenticate itself to Fyre server and request data, in the next section we will see what all APIs available and how to call them.


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