> For the complete documentation index, see [llms.txt](https://developers.lingk.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developers.lingk.io/lingk-apis/using-postman.md).

# 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)