# Using Postman with Lingk APIs

You can use Postman to test Lingk API calls before embedding them into Lingk recipes or into your application.

## Example configuration of an HTTP POST to the Lingk Event REST API

![](/files/-M3s1jS2trYW256SrGOh)

In an environment, create the following variables:

* `client-key`
* `client-secret`

The values for `client-key` and `client-secret` from your Lingk Workspace's "Overview" > "Settings" tab.

## The *Pre-request Script* for Lingk Auth

```javascript
function computeHttpSignature(config, headerHash) {
  var template = 'keyid="${keyId}",algorithm="${algorithm}",headers="${headers}",signature="${signature}"',
      sig = template;

  console.log(template); 
  console.log(headerHash); 

  // compute sig here
  var signingBase = '';
  config.headers.forEach(function(h){
    console.log(h);
    if (signingBase !== '') { signingBase += '\n'; }
    signingBase += h.toLowerCase() + ": " + headerHash[h];
  });

  console.log(signingBase); 

  var hashf = (function() {
      switch (config.algorithm) {
        case 'hmac-sha1': return CryptoJS.HmacSHA1;
        case 'hmac-sha256': return CryptoJS.HmacSHA256;
        case 'hmac-sha512': return CryptoJS.HmacSHA512;
        default : return null;
      }
    }());

  console.log("hashAlgorithm: " + config.algorithm);

  var hash = hashf(signingBase, config.secretkey);

  console.log("hash: " + hash);

  var signatureOptions = {
        keyId : config.keyId,
        algorithm: config.algorithm,
        headers: config.headers,
        signature : encodeURIComponent(CryptoJS.enc.Base64.stringify(hash))
      };

  console.log(signatureOptions); 

  // build sig string here
  Object.keys(signatureOptions).forEach(function(key) {
    var pattern = "${" + key + "}",
        value = (typeof signatureOptions[key] != 'string') ? signatureOptions[key].join(' ') : signatureOptions[key];
    sig = sig.replace(pattern, value);
  });
   console.log(sig); 

  return sig;
}


var curDate = new Date().toUTCString();
var targetUrl = request.url.trim(); // there may be surrounding ws
targetUrl = targetUrl.replace(new RegExp('^https?://[^/]+/'),'/'); // strip hostname
var method = request.method.toLowerCase();
var sha256digest = CryptoJS.SHA256(request.data);
var base64sha256 = CryptoJS.enc.Base64.stringify(sha256digest);
var computedDigest = 'sha-256=' + base64sha256;

var headerHash = {
      date : curDate,
      '(request-target)' : method + ' ' + targetUrl
    };

var config = {
      algorithm : 'hmac-sha1',
      keyId : environment['client-key'],
      secretkey : environment['client-secret'],
      headers : [ 'date', '(request-target)'  ]
    };

var sig = computeHttpSignature(config, headerHash);

postman.setEnvironmentVariable('httpsig', sig);
postman.setEnvironmentVariable("current-date", curDate);
```

## Troubleshooting

When the API response is an HTTP 410 "Clock skew outside of acceptable bounds", you may be behind a proxy server which filters the "Date" header. Therefore add an "x-aux-date" header and apply the same date header variable.

![](/files/-M3s1jS8HfECdSFomAED)


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://developers.lingk.io/lingk-apis/using-postman.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.