Clarification on -token-file option

Hello, just want to clarify is it expects a plain text in file, or I can pass HCL format like:

acl = {
  tokens = {
    agent = "f6b4182d-3dff-46a2-9a38-11a678f2b22b"
  }
}

It should be a plain text file with just the secret id of the token within it. Extra whitespace is trimmed though.