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
public:
  explicit UploadOwnedIOBufferElementReader(
      scoped_refptr<const net::IOBufferWithSize> buffer)
      : net::UploadBytesElementReader(buffer->data(), buffer->size()),
        buffer_(buffer) {}
  ~UploadOwnedIOBufferElementReader() override {}
  static UploadOwnedIOBufferElementReader* CreateWithBuffer(
      scoped_refptr<const net::IOBufferWithSize> buffer) {
    return new UploadOwnedIOBufferElementReader(std::move(buffer));
  }
 private:
  scoped_refptr<const net::IOBuffer> buffer_;
  DISALLOW_COPY_AND_ASSIGN(UploadOwnedIOBufferElementReader);
};
}  
AtomURLRequest::AtomURLRequest(api::URLRequest* delegate)
    : delegate_(delegate),
      is_chunked_upload_(false),
      response_read_buffer_(new net::IOBuffer(kBufferSize)) {}
AtomURLRequest::~AtomURLRequest() {