func injectCorrelationID(ctx context.Context, md *metadata.MD) context.Context {
	if hdr, ok := ctx.Value(correlationID).(string); ok {
		fmt.Printf("\tClient found correlationID %q in context, set metadata header\n", hdr)
		(*md)[string(correlationID)] = append((*md)[string(correlationID)], hdr)
	}
	return ctx
}
/* client before functions
package test
import (
	"context"
	"fmt"
	"google.golang.org/grpc/metadata"
)
type metaContext string
const (
	correlationID     metaContext = "correlation-id"
	responseHDR       metaContext = "my-response-header"
	responseTRLR      metaContext = "my-response-trailer"
	correlationIDTRLR metaContext = "correlation-id-consumed"
)