Setting playground headers programmatically.

[michaelyiu]

Hi, I was wondering if you were able to do this at all. I've seen a couple of sources such as:

apollographql/apollo-server#1982

and

graphql/graphql-playground#788

but unfortunately haven't been able to re-purpose it for the repo/example you've built. Making the whole token copy and pasting programmatic for the graphql playground would be such a huge plus and time saver!