Issue #41 Some simple notes on Accept.JS

Author: judgej

README.md

@@ -36,9 +36,46 @@ The following gateways are provided by this package:
 * AuthorizeNet_SIM
 * AuthorizeNet_DPM
 
+In addition, `Accept.JS` is supported by the AIM driver. More details are provided below.
+
 For general usage instructions, please see the main [Omnipay](https://github.com/thephpleague/omnipay)
 repository.
 
+## Accept.JS
+
+This gateway uses a JacaScript script to tokenize credit card details at the front end,
+i.e. in the payment form.
+Just the tokenized version of the credit card is then sent back to the merchant site,
+where it is used as a proxy for the credit card.
+
+The card is tokenized into two values returned in `opaqueData` object from Accept.JS:
+
+* dataDescriptor - the type of opaque data, e.g. "COMMON.ACCEPT.INAPP.PAYMENT"
+* dataValue - the value for the opaque data, e.g. "eyJjb2RlIjoiNT... {256 characters} ...idiI6IjEuMSJ9"
+
+These two values must be POSTed back to the merchant application, usually as a part of the payment form.
+Make sure the raw credit card details are NOT posted back to your site.
+How this is handled is beyond this short note, but examples are always welcome in the documentation.
+
+On the server, the tokenized detailt are passed into the `payment` or `authorize` request object.
+You will still need to pass in the `CreditCard` object, as that contains details of the payee and
+recipient, but just leave the credit card details of that object blank. For example:
+
+```php
+// $gateway is an instantiation of the AIM driver.
+// $dataDescriptor and $dataValue come from the paymentr form at the front end.
+
+$request = $gateway->purchase(
+    [
+        'notifyUrl' => '...',
+        'amount' => $amount,
+        'opaqueDataDescriptor' => $dataDescriptor,
+        'opaqueDataValue' => $dataValue,
+        ...
+    ]
+);
+```
+
 ## Support
 
 If you are having general issues with Omnipay, we suggest posting on