Can't get session ID (externalKey)
My application needs to access the `sid` on first render and right now the only "supported" way it can get access to that is after it has been saved which happens after the page is rendered.

I can get it this way:
```
const sym = Object.getOwnPropertySymbols(ctx)[0];
ctx[sym].externalKey
```
(Could also add a filter on the array to find the symbol that has "context#contextSession" as it's description for added safety)

but that seems awful.

Is there any other way to access the session ID before the request ends and it's saved to the backend?