``simple_httpclient`` (unsupported by ``curl_httpclient``).
Overrides ``validate_cert``, ``ca_certs``, ``client_key``,
and ``client_cert``.
- :arg bool allow_ipv6: Use IPv6 when available? Default is false in
- ``simple_httpclient`` and true in ``curl_httpclient``
+ :arg bool allow_ipv6: Use IPv6 when available? Default is true.
:arg bool expect_100_continue: If true, send the
``Expect: 100-continue`` header and wait for a continue response
before sending the request body. Only supported with