Ability to set a secret header for the IntrospectionQuery sent when running metadata apply or reload

[nrako]

I understand that Hasura Remote Schema Joins function needs to be able to introspect the remote GraphQL endpoint. I'd however love to have the ability to prevent everyone to introspect any GraphQL schemas which are joined. Some schemas are not meant to be public and inspectable by everyone.

It would be great if through either a Hasura CLI argument or a dedicated HASURA_ENV_VAR.. it'd be possible to set a secret which would be passed into the request header. This header could then be used to only authorize Hasura to introspect the schema (operationName: 'IntrospectionQuery') on the GraphQL endpoint.

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btw: the docs could be improved to make it clear that supporting introspection operation is required for adding a remote schema (and subsequent hasura metadata apply or hasura metadata reload)