DSC resource model versus ARM keys inconsistencies

[Gijsreyn]

Whilst working on #1286, I noticed inconsistencies between the ARM language versus what we can define in DSC. For example, here's a raw ARM template:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",

  "parameters": {
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    },
    "keyIndex": {
      "type": "int",
      "defaultValue": 0,
      "allowedValues": [0, 1]
    }
  },

  "resources": [
    {
      "type": "Microsoft.CognitiveServices/accounts",
      "apiVersion": "2023-05-01",
      "name": "myCogService",
      "location": "[parameters('location')]",
      "sku": {
        "name": "S0"
      },
      "kind": "CognitiveServices",
      "properties": {}
    },

    {
      "type": "Microsoft.Insights/components",
      "apiVersion": "2020-02-02",
      "name": "myAppInsights",
      "location": "[parameters('location')]",
      "properties": {
        "Application_Type": "web",

        "CognitiveApiKey": "[reference(resourceId('Microsoft.CognitiveServices/accounts', 'myCogService')).keys[parameters('keyIndex')].value]"
      }
    }
  ],

  "outputs": {
    "selectedKey": {
      "type": "string",
      "value": "[reference(resourceId('Microsoft.CognitiveServices/accounts', 'myCogService')).keys[parameters('keyIndex')].value]"
    }
  }
}

In one of the test cases, we built up:

$schema: https://aka.ms/dsc/schemas/v3/bundled/config/document.json
resources:
- name: "[format('Source-{0}', copyIndex())]"
  copy:
    name: sourceLoop
    count: 2
  type: Microsoft.DSC.Debug/Echo
  properties:
    output: "[concat('Value-', string(copyIndex(100)))]"
- name: "[format('Target-{0}', copyIndex())]"
  copy:
    name: targetLoop
    count: 2
  type: Microsoft.DSC.Debug/Echo
  properties:
    output: "[concat('Copied: ', reference(resourceId('Microsoft.DSC.Debug/Echo', format('Source-{0}', copyIndex()))).output)]"
  dependsOn:
  - "[resourceId('Microsoft.DSC.Debug/Echo', format('Source-{0}', copyIndex()))]"

I was wondering if this is "as expected" that we don't use .keys[]?