PLU-393: Variables: keys with . may be single key or nested path (#831)

### TL;DR
New MyInfo Child fields from FormSG returns data with `.` as part of the
key (e.g., `child.birthdate`).

Libraries like `lodash.get` treat `.` as a path separator for nested
properties (e.g., accessing `child.birthdate`), leading to incorrect
value retrieval or failure.

### What changed?
- Replaced the `.` in keys with `_` to avoid issues with obtaining
values.

### How to test?
1. Run the test suite to verify all scenarios pass
2. Test with actual FormSG fields from MyInfo Child

### Why make this change?
The standard lodash.get function doesn't properly handle cases where
object keys contain dots, leading to incorrect property access. This
implementation provides more accurate property resolution.

packages/backend/src/apps/formsg/__tests__/auth/decrypt-form-response.test.ts

@@ -410,6 +410,98 @@ describe('decrypt form response', () => {
         }),
       )
     })
+
+    it('should parse form fields and replace dots with underscores in keys', async () => {
+      mockDecryptedSubmission({
+        responses: [
+          {
+            _id: 'question1.field.answer',
+            fieldType: 'textarea',
+            question: 'What do you eat for breakfast?',
+            answer: 'i eat lorem dimsum for breakfast',
+          },
+          {
+            _id: 'question2.field.answer',
+            fieldType: 'mobile',
+            question: 'What is your mobile number?',
+            answer: '+6591234567',
+          },
+        ],
+      })
+      await expect(decryptFormResponse($)).resolves.toEqual(true)
+      expect($.request.body).toEqual(
+        expect.objectContaining({
+          fields: {
+            question1_field_answer: {
+              fieldType: 'textarea',
+              question: 'What do you eat for breakfast?',
+              answer: 'i eat lorem dimsum for breakfast',
+              order: 1,
+            },
+            question2_field_answer: {
+              fieldType: 'mobile',
+              question: 'What is your mobile number?',
+              answer: '+6591234567',
+              order: 2,
+            },
+          },
+        }),
+      )
+      expect($.request.headers).toBeUndefined()
+      expect($.request.query).toBeUndefined()
+    })
+
+    it('should parse form fields and replace dots with underscores in keys', async () => {
+      mockDecryptedSubmission({
+        responses: [
+          {
+            _id: 'childrenbirthrecords.abc.childdateofbirth.0',
+            fieldType: 'children',
+            question: 'Child Date of birth',
+            answer: '31/03/2017',
+          },
+          {
+            _id: 'childrenbirthrecords.abc.childname.0',
+            fieldType: 'children',
+            question: 'Child Name',
+            answer: 'John Doe',
+          },
+          {
+            _id: 'question2.field.answer',
+            fieldType: 'mobile',
+            question: 'What is your mobile number?',
+            answer: '+6591234567',
+          },
+        ],
+      })
+      await expect(decryptFormResponse($)).resolves.toEqual(true)
+      expect($.request.body).toEqual(
+        expect.objectContaining({
+          fields: {
+            childrenbirthrecords_abc_childdateofbirth_0: {
+              fieldType: 'children',
+              question: 'Child Date of birth',
+              answer: '31/03/2017',
+              order: 1,
+            },
+            childrenbirthrecords_abc_childname_0: {
+              fieldType: 'children',
+              question: 'Child Name',
+              answer: 'John Doe',
+              order: 2,
+            },
+            question2_field_answer: {
+              fieldType: 'mobile',
+              question: 'What is your mobile number?',
+              answer: '+6591234567',
+              order: 3,
+            },
+          },
+        }),
+      )
+      expect($.request.headers).toBeUndefined()
+      expect($.request.query).toBeUndefined()
+    })
   })
 
   describe('attachments', () => {

packages/backend/src/apps/formsg/auth/decrypt-form-response.ts

@@ -121,7 +121,9 @@ export async function decryptFormResponse(
 
       // Note: the order may not be sequential; fields (e.g. NRIC) can be
       // omitted from the output.
-      parsedData[_id] = {
+      // Note: FormSG uses dot notation for field ids for MyInfo children
+      // we replace with underscore to avoid issues when using lodash get.
+      parsedData[_id.replaceAll('.', '_')] = {
         order: index + 1,
         ...rest,
       }

packages/backend/src/helpers/__tests__/compute-parameters.test.ts

@@ -319,4 +319,34 @@ describe('compute parameters', () => {
     const result = computeParameters(params, executionStep)
     expect(result).toEqual(expected)
   })
+
+  it('should process parameters with underscores in keys', () => {
+    const executionStep = [
+      {
+        stepId: randomStepID,
+        dataOut: {
+          childrenbirthrecords_abc_childdateofbirth_0: {
+            fieldType: 'children',
+            question: 'Child Date of birth',
+            answer: '31/03/2017',
+            order: 1,
+          },
+          childrenbirthrecords_abc_childname_0: {
+            fieldType: 'children',
+            question: 'Child Name',
+            answer: 'John Doe',
+            order: 2,
+          },
+        },
+      } as unknown as ExecutionStep,
+    ]
+    const params = {
+      toSubstitute: `{{step.${randomStepID}.childrenbirthrecords_abc_childdateofbirth_0.answer}} {{step.${randomStepID}.childrenbirthrecords_abc_childname_0.answer}}`,
+    }
+    const expected = {
+      toSubstitute: `31/03/2017 John Doe`,
+    }
+    const result = computeParameters(params, executionStep)
+    expect(result).toEqual(expected)
+  })
 })