How can I achieve a shared context across a federated graph?

I'm looking for some way to pass context about what 1 microservice resolved to the following microservices involved in serving the request.
```
Thing { # resolved by microservice 1
id
name
items {
id
name
stuff { # resolved by microservice 2
id
foo {
bar { # resolved by microservice 3
...barFields
}
}
}
}
}
```
In order for microservice 2 to resolve the fields of `stuff`, `items'` `stuff` field resolver must return something like
`{ id: item.stuffId}`.

In order for microservice 3 to resolve the fields of `bar`, `foo's` `bar` field resolver must return something like
`{ id: stuff.barId}`.

that all works just fine, but what if i wanted `barFields` in microservice 3 to have context about the `item` back in microservice 1?

From what I've observed so far, returning other fields besides `id` or `__typename` will be dropped when the request continues to the next microservice

查看 federated gateway 以及它如何在服务之间传递上下文。issue 提到，除 id 和 __typename 之外的额外字段会被丢弃。首先检查 gqlgen 中 federation plugin 的代码，尤其是 federation package 以及它如何处理实体表示。查看 federation specification 中关于上下文传递的内容。第一步应当是编写一个能够复现字段丢弃的 test。

由索引模型根据 Issue 内容生成。