Missing Authentication Header in Proxy

[lovelydinosaur]

Discussed in #1959

^{Originally posted by lebr0nli December 2, 2021}
I follow httpx doc

>>> httpx.get('http://google.com/', proxies={'http://':'http://aaaa:bbbb@127.0.0.1:8030'})

Although:

>>> httpx.Proxy('http://aaaa:bbbb@127.0.0.1:8030')
Proxy(url='http://127.0.0.1:8030', headers={'proxy-authorization': 'Basic YWFhYTpiYmJi'})

I got:

GET http://google.com/ HTTP/1.1
Host: google.com
Accept: */*
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
User-Agent: python-httpx/0.21.1

There is no Proxy-Authorization.
Did I miss using something?
Thanks!