errors do not conform to the GraphQL specification

[oliverpool]

Describe the bug

According to the end of 7.1.2 Errors, non-standard fields should be put under extensions in case of error.

Currently when returning an error, this extension behaves like the counter example and sets code, fields, short_message and vars directly:

{
  "data": null,
  "errors": [
    {
      "code": "forbidden",
      "fields": [],
      "locations": [{ "column": 3, "line": 2 }],
      "message": "forbidden",
      "path": ["some_path"],
      "short_message": "forbidden",
      "vars": {}
    }
  ]
}

To Reproduce
Setup a GraphQL server and perform a request which triggers an authentication failure.

Expected behavior
The non-standard fields should be put under an extensions key:

{
  "data": null,
  "errors": [
    {
      "locations": [{ "column": 3, "line": 2 }],
      "message": "forbidden",
      "path": ["some_path"],
      "extensions": {
        "code": "forbidden",
        "fields": [],
        "short_message": "forbidden",
        "vars": {}
      }
    }
  ]
}

To not break backward compatibility while providing support for spec-compliant clients, the fields could be duplicated in the meantime:

{
  "data": null,
  "errors": [
    {
      "locations": [{ "column": 3, "line": 2 }],
      "message": "forbidden",
      "path": ["some_path"],

      "code": "forbidden",
      "fields": [],
      "short_message": "forbidden",
      "vars": {}
      "extensions": {
        "code": "forbidden",
        "fields": [],
        "short_message": "forbidden",
        "vars": {}
      }
    }
  ]
}

Additional context
I am querying the GraphQL server with a Go client which discards non-standard keys not put under extensions: https://pkg.go.dev/github.com/vektah/gqlparser/v2@v2.5.17/gqlerror#Error

[zachdaniel]

Thanks for the report! There is no harm in adding it to both places. I won't have time to do this in the near future, but PRs welcome 🙇