Add OAuth2 support

[arondaniel]

Problem description

It would be nice to use smart_open to access OAuth2 URLs. In my case I needed to access resources using NASA URS.

I'm new to this library but I couldn't find a way to make this work directly using your API (without registering a new http/https handler).

I was able to make it work pretty easily by passing in my own requests.Session object into the http.py open method and storing that in the io.BufferedIOBase subclasses. Then, I just use that Session object in the two "get" calls if it's not None.

The Session object I used worked for me. Not sure if it works for other OAuth hosts:

  class URSSession(requests.Session):

    auth_host = None
    def __init__(self, auth_host, username, password):
        super().__init__()
        self.auth_host = auth_host
        self.auth = (username, password)

    # Overrides from the library to keep headers when redirected to or from
    # the NASA auth host.
    def rebuild_auth(self, prepared_request, response):

      headers = prepared_request.headers
      url = prepared_request.url

      if 'Authorization' in headers:
        original_parsed = requests.utils.urlparse(response.request.url)
        redirect_parsed = requests.utils.urlparse(url)

        if (original_parsed.hostname != redirect_parsed.hostname) and \
              redirect_parsed.hostname != self.auth_host and \
              original_parsed.hostname != self.auth_host:
                del headers['Authorization']
        return

So... if others may want to do this, maybe it would be good to make http handler take an optional requests.Session?

Steps/code to reproduce the problem

None, just a suggestion for improvement.

Versions

macOS-12.6.7-arm64-arm-64bit Python 3.10.11 | packaged by conda-forge | (main, May 10 2023, 19:01:19) [Clang 14.0.6 ] smart_open 6.4.0

[mpenkov]

Are you interested in doing a PR?