How to modify querie's arguments in a wrapped schema

[javobal]

Hi All!

I am trying to wrap a remote graphql api (saleor's) and enforce some custom authorization rules on top of it, and i would like to modify the incoming queries according to the user's access level.

My first step was to test if i was able to expose only parts of the saleor's graphql endpoint, that went well with FilterRootFields. Then my next step was to test if could read and modify passed arguments to those exposed operations, so far i have achieved this using TransformObjectFields but i think i am not using it the way it is supposed to. Do i need to create a custom Transform for this ? or maybe use stitched schemas ?

So any guidance in the right direction would be appreciated

import fetch from 'node-fetch'
import { print, StringValueNode, ArgumentNode } from 'graphql'
import { ExecutionParams } from '@graphql-tools/utils'
import { introspectSchema, wrapSchema, TransformObjectFields, FilterRootFields } from '@graphql-tools/wrap'
import config from 'lib/config'

const executor = async ({ document, variables }: ExecutionParams) => {
  const query = print(document)
  const fetchResult = await fetch(config.saleor.admin_endpoint, {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${config.saleor.admin_api_token}`,
    },
    body: JSON.stringify({ query, variables }),
  })
  return fetchResult.json()
}

export default async () => {
  const schema = wrapSchema({
    schema: await introspectSchema(executor),
    transforms: [
      new FilterRootFields((operationName, fieldName) => { // Expose only Query.products and Mutation.productCreate
        if (operationName === 'Query' && fieldName === 'products') return true 
        if (operationName === 'Mutation'&& fieldName === 'productCreate') return true
        return false
      }),
      new TransformObjectFields( // 
        (typeName, fieldName, fieldConfig) => {
          return fieldConfig
        },
        (typeName, fieldName, fieldConfig) => {
          // Modify Query.products graphQL Request
          if (typeName === 'Query' && fieldName === 'products') { // modify Query.products arguments

            // Find the first channel argument
            const channelArg = fieldConfig.arguments?.find((arg) => arg.name.value === 'channel')
            if (channelArg) {
              const valueArg = channelArg?.value as unknown as StringValueNode

              const newArgument = {
                kind: 'Argument',
                name: channelArg.name,
                value: {
                  kind: 'StringValue',
                  value: 'test-retailer', // 13 characters
                  block: false,
                  loc: { start: valueArg.loc?.start, end: valueArg.loc?.start || 0 + 2 + 13} // confused here, i just manually sum the value characters length since it seems to be doing that
                }
              } as ArgumentNode

              // Filter out all possible instances of a channel argument
              const newArguments = fieldConfig.arguments?.filter((arg) => arg.name.value !== 'channel').slice(0)
              newArguments?.push(newArgument)

              return {
                kind: 'Field',
                arguments: newArguments,
                name: fieldConfig.name,
                selectionSet: fieldConfig.selectionSet,
              } as typeof fieldConfig
            }
          }
          return fieldConfig
        }
      ),
    ],
    executor,
  })
  return schema
}