Server side validation on fields

[gerhardcit]

Is your feature request related to a problem? Please describe.
When filling in values in a form, I need to validate fields by doing some remote fetch on the server to see if it's valid.

Describe the solution you'd like
How do I set errors on the server side for a field and send it back to the client?

Describe alternatives you've considered
Tried something like this

const adminValue = form.data.admin;
const valid = await validateAdmin(adminValue);
if (!valid) {
    form.errors.admin = ['Invalid admin version'];
    return fail(400, form);
}

Additional context
Often form input would require some lookups and double checking before we can accept the form.
Not sure I'm missing something, but the docs does not seem to be clear on that?

[gerhardcit]

Documentation shows this

if (form.data.email.includes('spam')) {
      // Will also return fail, since status is >= 400
      // form.valid will also be set to false.
      return message(form, 'No spam please', {
        status: 403
      });
    }

should it not be able to attach the "No spam please" message to the email errors ?

[gerhardcit]

ok, found it..

if (!valid) {
    form.errors.admin = ['Invalid admin version'];
    return fail(400, {form});
}

duh...

[ciscoheat]

setError is also a convenient way of setting form errors.