Close #19494: add urrlib.request.HTTPBasicPriorAuthHandler

This auth handler adds the Authorization header to the first
HTTP request rather than waiting for a HTTP 401 Unauthorized
response from the server as the default HTTPBasicAuthHandler
does.

This allows working with websites like https://api.github.com which do
not follow the strict interpretation of RFC, but more the dicta in the
end of section 2 of RFC 2617:

    > A client MAY preemptively send the corresponding Authorization
    > header with requests for resources in that space without receipt
    > of another challenge from the server.  Similarly, when a client
    > sends a request to a proxy, it may reuse a userid and password in
    > the Proxy-Authorization header field without receiving another
    > challenge from the proxy server. See section 4 for security
    > considerations associated with Basic authentication.

Patch by Matej Cepl.

1 files changed, 11 insertions, 0 deletions

diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index f42025961f..dca56d6e04 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -304,6 +304,17 @@ The following classes are provided:
    presented with a wrong Authentication scheme.
 
 
+.. class:: HTTPBasicPriorAuthHandler(password_mgr=None)
+
+   A variant of :class:`HTTPBasicAuthHandler` which automatically sends
+   authorization credentials with the first request, rather than waiting to
+   first receive a HTTP 401 "Unauthorised" error response. This allows
+   authentication to sites that don't provide a 401 response when receiving
+   a request without an Authorization header. Aside from this difference,
+   this behaves exactly as :class:`HTTPBasicAuthHandler`.
+
+   .. versionadded:: 3.5
+
 .. class:: ProxyBasicAuthHandler(password_mgr=None)
 
    Handle authentication with the proxy. *password_mgr*, if given, should be