function throwIfProxyAuthIsSent (headers) {
  const existProxyAuth = headers && Object.keys(headers)
    .find((key) => key.toLowerCase() === 'proxy-authorization')
  if (existProxyAuth) {
    throw new InvalidArgumentError('Proxy-Authorization should be sent in ProxyAgent constructor')
  }
}
@param {Record<string, string>} headers

Previous versions of ProxyAgent suggests the Proxy-Authorization in request headers
Nevertheless, it was changed and to avoid a security vulnerability by end users
this check was created.
It should be removed in the next major version for performance reasons