func WithConfigContext(ctx context.Context, cfg *config.Config) context.Context {
	return withKeyContext(ctx, cfgKey, cfg)
}
WithConfigContext wraps a config object into context.
package middleware
import (
	"context"
	"net/http"
	"github.com/sirupsen/logrus"
	"github.com/dcos/dcos-go/dcos/nodeutil"
	"github.com/dcos/dcos-log/dcos-log/config"
)
type key int
const (
	cfgKey key = key(iota)
	httpClientKey
	nodeInfoKey
	tokenKey
)
func withKeyContext(ctx context.Context, k key, obj interface{}) context.Context {
	return context.WithValue(ctx, k, obj)
}
func fromContextByKey(ctx context.Context, k key) (interface{}, bool) {
	instance := ctx.Value(k)
	return instance, instance != nil
}