always save original $data to $_source

[nick-sun-balance]

Environment:
OS: Ubuntu 14.04
Web server: Nginx 1.9.7
PHP version: 7.0.2 (as FPM)

Issue:
Braintree payment method cannot be used during checkout.

More details:

When using "Braintree" as payment method, the javascript object "window.checkoutConfig.payment.braintree" has no value for "clientToken" which will result the payment method not visible on checkout page plus a javascript error.

After further investigation, the reason has been located at:
File:
lib/internal/Magento/Framework/App/Config/Data.php

In "__construct", passed parameter "$data" has been manipulated after being passed to "process" method of "$processor" object especially values which should be kept as "encrypted" for the "$_source" property.

These values include but not limited to:
"$data['payment']['braintree']['public_key']"

Making calls to "var_dump($data['payment']['braintree']['public_key']);" before and after "$processor->process($data);" will see different values.

The result is that the value of "payment/braintree/public_key" being passed from data table "core_config_data" to "frontend" usage has been decrypted TWICE (due to values are passed through base -> website -> store as "scope"). So the curl request sent to Braintree will result a "401" error (unauthorised) due to wrong keys have been passed.

The code change I composed could not be the best solution but has been local tested and it works. Please advise if a better solution should be applied.

Thanks Magento team!

[dsikkema-magento]

Hi @nick-sun-balance, thanks for the report and the contribution. This looks to be the same as #2984, and we have made some changes which should resolve the issue for now. I'm going to close the ticket, but if you still find the same problem on the develop branch, please go ahead and re-open it and we'll take a look.