let env_value = match env_key {
      Some(env_key) => match env::var(format!("ORD_{env_key}")) {
        Ok(env_value) => Some(env_value),
        Err(err @ env::VarError::NotUnicode(_)) => return Err(err.into()),
        Err(env::VarError::NotPresent) => None,
      },
      None => None,
    };

    Ok(
      arg_value
        .or(env_value.as_deref())
        .or(config_value)
        .or(default_value)
        .map(str::to_string),
    )
  }

  pub(crate) fn auth(&self) -> Result<Auth> {
    let config = self.load_config()?;

    let rpc_user = Options::derive_var(
      self.bitcoin_rpc_user.as_deref(),
      Some("BITCOIN_RPC_USER"),
      config.bitcoin_rpc_user.as_deref(),
      None,
    )?;

    let rpc_pass = Options::derive_var(
      self.bitcoin_rpc_pass.as_deref(),
      Some("BITCOIN_RPC_PASS"),
      config.bitcoin_rpc_pass.as_deref(),
      None,
    )?;

    match (rpc_user, rpc_pass) {
      (Some(rpc_user), Some(rpc_pass)) => Ok(Auth::UserPass(rpc_user, rpc_pass)),
      (None, Some(_rpc_pass)) => Err(anyhow!("no bitcoind rpc user specified")),