Secret function doesn't honour at-sign (@) to load file contents into an attribute

[tomwerneruk]

Consul Template version

compiled from main @ commit 51401f3

Configuration

vault {
  address = "http://127.0.0.1:8200"
}

template {
  source      = "./in.tmpl"
  destination = "./out.cer"
}

{{ with secret "pki_int/sign/example-dot-com" "ttl=60s" "csr=@./MYCSR.csr" }}
{{ .Data.certificate }}
{{ end }}

Command

consul-template -template "in.tmpl:out.cer"
or
consul-template -config config.hcl 

Expected behavior

The Vault convention of prefixing a file with an @ then causes the contents to be read and used as the value

Actual behavior

The string is used literally, passing the value '@./MYCSR.csr' to Vault, causing an HTTP 400

Steps to reproduce

1. Create a template and CSR as above
2. Configure Vault using https://learn.hashicorp.com/tutorials/vault/pki-engine?in=vault/secrets-management
3. Execute consul-template against Vault