Deploy an Azure Role Assignment to grant a User-Assigned Managed Identity access to Storage Account

arm-template.json

// Based on https://docs.microsoft.com/en-us/azure/role-based-access-control/role-assignments-template#resource-scope
[
  {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2019-06-01",
      "name": "[variables('myStorageAccountName')]",
      "location": "[variables('location')]",
      "sku": {
          "name": "Standard_LRS"
      },
      "properties": {
          "supportsHttpsTrafficOnly": true
      }
  },
  {
      "type": "Microsoft.Storage/storageAccounts/providers/roleAssignments",
      "apiVersion": "2018-09-01-preview",
      "name": "[concat(variables('myStorageAccountName'), '/Microsoft.Authorization/', guid(uniqueString(variables('myStorageAccountName'))))]",
      "properties": {
          "_comment1": "Role definition IDs from: https://docs.microsoft.com/en-us/azure/role-based-access-control/built-in-roles#storage",
          "roleDefinitionId": "[concat('/subscriptions/', subscription().subscriptionId, '/providers/Microsoft.Authorization/roleDefinitions/', 'b24988ac-6180-42a0-ab88-20f7382dd24c')]",
          "_comment2": "Something like: /subscriptions/my-subscription/resourceGroups/my-other-resource-group/providers/Microsoft.ManagedIdentity/userAssignedIdentities/myManagedIdentity",
          "principalId": "[reference(parameters('myManagedIdentity'), '2018-11-30').principalId]"
      },
      "dependsOn": [
          "[concat('Microsoft.Storage/storageAccounts/', variables('myStorageAccountName'))]"
      ]
  },
  {
      "type": "Microsoft.Web/sites",
      "apiVersion": "2018-11-01",
      "name": "[variables('myWebSiteName')]",
      "location": "[variables('location')]",
      "identity": {
          "type": "UserAssigned",
          "userAssignedIdentities": {
              "[parameters('myManagedIdentity')]": { }
          }
      },
      "dependsOn": [
          "[concat('Microsoft.Web/serverfarms/', variables('myServerFarmName'))]",
          "[concat('Microsoft.Storage/storageAccounts/', variables('myStorageAccount'))]"
      ],
      "properties": {
          "name": "[variables('myWebSiteName')]",
          "serverFarmId": "[resourceId('Microsoft.Web/serverFarms',variables('myServerFarmName'))]"
      }
  }
]