Confusing error message if credentials_service_account() pointing at incorrect file

[MarkEdmondson1234]

One of the most common errors I've seen when authenticating with service accounts is that user's try to use the client JSON rather than the service account key JSON.

If I replicate this behaviour with credentials_service_account() I get an error that the file is not present, rather than it is present but the wrong file.

path <- "../../auth/client.json"
credentials_service_account(scopes = "email", path = path)
Error in read_input(file) : 
  file must be connection, raw vector or file path
> file.exists(path)
# TRUE

To help with this I check for the presence for $private_key in the JSON file, to help give a hint:

  secrets  <- fromJSON(json_file)
  
  if(is.null(secrets$private_key)){
    stop("$private_key not found in JSON - have you downloaded the correct JSON file? 
         (Service Account Keys, not service account client)")
  }