Add a section for setting up postman

Author: Jaspaul

readme.md

@@ -68,3 +68,42 @@ Route::get('/fire', function () {
     return "You'll only see this if the signature of the request is valid!";
 })->middleware('verify-signature');
 ```
+
+### Signing Postman Requests
+
+If you, like us, like to use [postman](https://www.getpostman.com/) to share your api internally you can use the following pre-request script to automatically sign your postman requests:
+
+```js
+function guid() {
+  function s4() {
+    return Math.floor((1 + Math.random()) * 0x10000)
+      .toString(16)
+      .substring(1);
+  }
+  return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
+    s4() + '-' + s4() + s4() + s4();
+}
+
+postman.setEnvironmentVariable("x-signed-id", guid());
+postman.setEnvironmentVariable("x-signed-timestamp", (new Date()).toUTCString());
+postman.setEnvironmentVariable("x-algorithm", "sha256");
+
+var payload = {
+    "id": postman.getEnvironmentVariable("x-signed-id"),
+    "method": request.method,
+    "timestamp": postman.getEnvironmentVariable("x-signed-timestamp"),
+    "uri": request.url.replace("{{url}}", postman.getEnvironmentVariable("url")),
+    "content": (Object.keys(request.data).length === 0) ? "" : request.data
+};
+
+var hash = CryptoJS.HmacSHA256(JSON.stringify(payload), postman.getEnvironmentVariable("key"));
+var signature = hash.toString();
+
+postman.setEnvironmentVariable("x-signature", signature);
+```
+
+Note for this to work you'll have to setup your environment to have the following variables:
+    - `{{url}}` this is the base url to the api you'll be hitting.
+    - `{{key}}` this is the shared secret key you'll be using in your environment.
+
+All other environment variables that will be needed will be automatically generated by the above script.