fix: custom api does not work when step parameter is the JSON body itself (#1281)

## Problem
Custom API body does not work when the step parameter is the body.
The computed variable from the step parameter is not being parsed
properly.

## Solution
* Attempt to parse the variable as a valid JSON first
* Only strip the extra " from the start and end of the string if its not
a valid JSON as the user would have already wrapped it in "

## How to test?
- [ ] Works when body is a manually configured JSON, i.e., variables are
used as the key or value in the JSON object
- [ ] Works when the body is a JSON object from a step variable

Author: kevinkim-ogp

packages/backend/src/apps/custom-api/actions/http-request/index.ts

@@ -91,8 +91,21 @@ const action: IRawAction = {
 
   preprocessVariable(parameterKey: string, variableValue: unknown) {
     if (parameterKey === 'data' && typeof variableValue === 'string') {
+      // check if the variable is a valid JSON
+      if (variableValue.startsWith('{') || variableValue.endsWith('}')) {
+        try {
+          JSON.parse(variableValue as string)
+          // its a valid JSON, don't need to do anything extra
+          return variableValue
+        } catch (e) {
+          // not a valid JSON, remove the " from the start and end of the string
+          return JSON.stringify(variableValue).slice(1, -1)
+        }
+      }
       // NOTE: this removes the " from the start and end of the string
       // as it is already added in the user input
+      // when user forms the JSON on the frontend:
+      // {"key": "<variable>"}
       return JSON.stringify(variableValue).slice(1, -1)
     }
     return variableValue