kubernetes/vendor/google.golang.org/grpc/internal/grpcutil/metadata.go

type mdExtraKey …

// WithExtraMetadata creates a new context with incoming md attached.
func WithExtraMetadata(ctx context.Context, md metadata.MD) context.Context { … }

// ExtraMetadata returns the incoming metadata in ctx if it exists.  The
// returned MD should not be modified. Writing to it may cause races.
// Modification should be made to copies of the returned MD.
func ExtraMetadata(ctx context.Context) (md metadata.MD, ok bool) { … }