add documentation for Cookie

Author: sunny-chung

CHANGELOG.md

@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 _Changes since 1.7.3_
 
 ### Added
+- Cookie support (Default disabled. Enable in the Subproject Configuration Dialog)
 - On pre-flight, update environment variables according to request headers, query parameters and bodies
 - A "Save Raw" button at the response viewer to save raw response body to a file
 

doc/_include/cookie-editor-1-in-environment.png

@@ -0,0 +1,51 @@
+---
+title: Cookie
+---
+
+# HTTP Cookie
+
+## Enable or Disable
+
+To enable Cookie support, first enable in the Subproject Configuration dialog. It would affect the whole Subproject.
+
+By default, Cookie is disabled.
+
+![Enable Cookie Step 1](../cookie-enable-step-1.png)
+
+![Enable Cookie Step 2](../cookie-enable-step-2.png)
+
+## Receive Cookie
+
+To receive Cookie from servers, an environment must be selected or created. Cookie storage is not shared among multiple environments.
+
+## Send Cookie
+
+If Cookie is enabled, the Cookie storing in the storage would be applied to matching requests automatically. To examine what Cookie would be applied, check the Cookie tab in the Request Example level.
+
+To send custom Cookie in additional to stored Cookie, one can insert Cookie in the Cookie tab in the Request Example level:
+
+![Cookie Editor in Request Example](../cookie-editor-in-request-example.png)
+
+or in the Environment level:
+
+![Cookie Editor 1 in Environment](../cookie-editor-1-in-environment.png)
+
+![Cookie Editor 2 in Environment](../cookie-editor-2-in-environment.png)
+
+## Variables and Functions
+
+Variables and functions are supported only in the "value" field.
+
+However, Cookie containing variable and function macros in the "Set-Cookie" response headers are automatically dropped for security reasons.
+
+For example, in the following response, only the cookie "cookie1" would be stored.
+
+```
+HTTP/1.1 204 No Content
+Set-Cookie: cookie0=some-${{var}}; Max-Age=3600
+Set-Cookie: cookie1=AbcDE; Max-Age=3600
+```
+
+## Applicable Transports
+
+All types of supported HTTP transport, including WebSocket, GraphQL and gRPC, support Cookie. Note that response headers "Set-Cookie" only take effect after the entire request is completed.

doc/_include/cookie-editor-2-in-environment.png

@@ -15,6 +15,7 @@ navigation:
       - path: doc/features/environments.md
       - path: doc/features/ssl-configuration.md
       - path: doc/features/functions.md
+      - path: doc/features/cookie.md
       - path: doc/features/user-script.md
       - path: doc/features/post-flight-actions.md
       - path: doc/features/viewing-responses.md