Reactive custom constraint validator in spring webflux - reactive-programming

Question

I'm trying to write a custom ConstraintValidator which does a mongodb lookup using spring-webflux and spring-data reactive mongo.
In traditional spring webmvc, one would create a) an annotation and b) implement a custom ConstraintValidator, then annotate the #RequestBody with #Valid, and spring webmvc would
call the validator and reject the request with status code 400 if the validation result is false.
However when using the same approach in spring webflux, i seem to be forced to implement the custom constraint validator in a blocking way, which does not fit the reactive model of spring webflux. Example (simplified for brevity):
public class UserPasswordValidator
implements ConstraintValidator<ValidUserPassword, UpdateUserPasswordDto> {
#Resource
private ReactiveUserRepository reactiveUserRepo;
#Override
public boolean isValid(UpdateUserPasswordDto userPasswordDto,
ConstraintValidatorContext context) {
// This is a blocking call. How can this be done in webflux?
UserEntity user = reactiveUserRepo.findByUuid(userPasswordDto.getUuid()).block();
if (!oldPasswordIsCorrect(userPasswordDto.getCurrentPassword(), user.getPasswordHash())) {
context.disableDefaultConstraintViolation();
context
.buildConstraintViolationWithTemplate("Incorrect current password")
.addConstraintViolation();
return false;
}
return true;
}
}
Is there a way to do custom validation which needs a database lookup in spring webflux in a non-blocking way?