Fix handling of default values in subject

[SpencerBrown]

When creating a new certificate request or self-signed certificate, the subject map has a number of fields, all of which are optional. provider.go has a function nameFromResourceData that creates a pkix.Name struct from the data in the subject map.

That function tests for missing values by comparing with nil. This is incorrect, as missing string values come through as "" and missing list values come through as []. The result of this error is that the following HCL produces a certificate with the Subject Name C=, ST=, L=/postalCode=, O=MongoDB, OU=, CN=Example CA:

resource "tls_private_key" "ca" {
  algorithm = "RSA"
  rsa_bits = 2048
}
resource "tls_self_signed_cert" "ca" {
  is_ca_certificate = true
  key_algorithm = "RSA"
  allowed_uses = [
    "cert_signing",
    "ocsp_signing"
  ]
  private_key_pem = "${tls_private_key.ca.private_key_pem}"
  "subject" {
    organization = "MongoDB"
    common_name = "Example CA"
  }
  validity_period_hours = 8760
}

With this fix, the Subject Name is O=MongoDB, CN=Example CA as it should be.

[apparentlymart]

Thanks for working on this, @SpencerBrown!

Looks good to me. Thanks for all of the thorough testing.

[github-actions]

I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.