Edge Encryption proxy does not support encryption of attachments uploaded through REST API

Description

Cannot upload/encrypt and download/decrypt an attachment via REST through the Edge Encryption proxy.

Log in as administrator in a pre-Kingston instance.
Activate the Edge Encryption plugin.
Set up a proxy pointing to the instance.
On the Service Portal, open a session using the Edge Encryption proxy.

Note that you can add attachments. Also, the generated [sys_attachment] records are not encrypted, and can be accessed in a session not using the Edge Encryption proxy.
Create an Incident record invoking a preprogrammed REST API (JS or C#NET) with a POST action and JSON format towards the Incident table.

Note that the call is unsuccessful and throws a Gateway Timeout error. The REST API call with the GET action to the Incident table might be successful and return records.

The workaround on pre-Kingston instances is to use POST requests to sys_attachment.do for REST attachments.

Headers needed: Content-Type and Authorization

Cookies needed: glide_user, glide_user_session, jsessionid

For example, your Cookie section should look like this example:

glide_user=<yourGlideUser>; glide_user_route=<yourGlideUserRoute>; JSESSIONID=<yourJsessionID>;

Content of the POST

The content of the POST should be in the format:

Content-Type: multipart/form-data; boundary=---------------------------12296202189918688451571609901

Content-Length: 56332

-----------------------------12296202189918688451571609901

Content-Disposition: form-data; name="sysparm_ck"

6129f3b2dbe5720057675404ce96199e82ac2a0497f83ca7c5307f72566b4004e4771c62

-----------------------------12296202189918688451571609901

Content-Disposition: form-data; name="sysparm_sys_id"

85071a1347c12200e0ef563dbb9a71c1

-----------------------------12296202189918688451571609901

Content-Disposition: form-data; name="sysparm_table"

incident

-----------------------------12296202189918688451571609901

Content-Disposition: form-data; name="attachFile"; filename="myFile.txt"

Content-Type: text/xml

-----------------------------12296202189918688451571609901--

Related Problem: PRB1164901