// I would recommend to use interceptors:// clientgrpc.Dial(target, grpc.WithPerRPCCredentials(&loginCreds{    Username: "admin",    Password: "admin123",}))type loginCreds struct {    Username, Password string}func (c *loginCreds) GetRequestMetadata(context.Context, ...string) (map[string]string, error) {    return map[string]string{        "username": c.Username,        "password": c.Password,    }, nil}func (c *loginCreds) RequireTransportSecurity() bool {    return true}// servergrpc.NewServer(    grpc.StreamInterceptor(streamInterceptor),     grpc.UnaryInterceptor(unaryInterceptor))func streamInterceptor(srv interface{}, stream grpc.ServerStream, info *grpc.StreamServerInfo, handler grpc.StreamHandler) error {    if err := authorize(stream.Context()); err != nil {        return err    }    return handler(srv, stream)}func unaryInterceptor(ctx context.Context, req interface{}, info *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (interface{}, error) {    if err := authorize(ctx); err != nil {        return err    }    return handler(ctx, req)}func authorize(ctx context.Context) error {    if md, ok := metadata.FromContext(ctx); ok {        if len(md["username"]) > 0 && md["username"][0] == "admin" &&            len(md["password"]) > 0 && md["password"][0] == "admin123" {            return nil        }        return AccessDeniedErr    }    return EmptyMetadataErr}