HttpServer.request.schemaBodyForm would be better if it allowed optional values

const RegistrationForm = S.union(
  S.struct({
    email: Email.schema,
    password: Password.Strong.schema,
    firstName: User.FirstName.schema,
    lastName: User.LastName.schema,
    optInMarketing: S.literal("on"),
  }),
  S.struct({
    email: Email.schema,
    password: Password.Strong.schema,
    firstName: User.FirstName.schema,
    lastName: User.LastName.schema,
  }),
);