Env var names referenced by providerConfig's {env.VAR} placeholders (or, for route53's default zero-arg call, consumed directly by the AWS SDK's credential chain).
OptionalproviderOmitted for providers (e.g. route53 when called with no explicit
options) that resolve credentials outside of providerConfig
entirely.
Result of building a provider's DNS-01 config: the typed
providerConfigto pass through to buildAcmeDnsPolicy.providerConfig, plus the env var names the caller should ensure are set (names only — never values).