Will be nice to clear auth credentials. For example, I'm using a proxy that accepts options via username:

```
proxy.com:8080
user: wiliam_country_US
```

So, if I want to change the peer node, I change my username:

```
proxy.com:8080
user: wiliam_country_GB
```

But, I'm not changing the proxy, so electron has valid credentials and is not going to trigger `login` event.

I'm searching the way to clean auth settings so electron asks them again.
atom/browser/net/atom_url_request.cc
const base::string16& username,
    const base::string16& password) const {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  if (username.empty() || password.empty()) {
    content::BrowserThread::PostTask(
        content::BrowserThread::IO, FROM_HERE,
        base::Bind(&AtomURLRequest::DoCancelAuth, this));
  } else {
    content::BrowserThread::PostTask(
        content::BrowserThread::IO, FROM_HERE,
        base::Bind(&AtomURLRequest::DoSetAuth, this, username, password));
  }
}
void AtomURLRequest::DoWriteBuffer(
    scoped_refptr<const net::IOBufferWithSize> buffer,
    bool is_last) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
  if (!request_) {
    return;
  }
  if (is_chunked_upload_) {
    
    bool first_call = false;
    if (!chunked_stream_writer_) {
      std::unique_ptr<net::ChunkedUploadDataStream> chunked_stream(
          new net::ChunkedUploadDataStream(0));
      chunked_stream_writer_ = chunked_stream->CreateWriter();
      request_->set_upload(std::move(chunked_stream));
      first_call = true;