Fix proxy headers use default headers

[junnplus]

What do these changes do?

Fix proxy headers use default headers, PR #2272 caused ClientHttpProxyError(Proxy Authentication Required) use proxy when Authorization in default headers.

Are there changes in behavior for the user?

no.

Related issue number

#2272

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bug)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov-io]

Codecov Report

Merging #2487 into 2.3 will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              2.3    #2487      +/-   ##
==========================================
- Coverage   97.25%   97.25%   -0.01%     
==========================================
  Files          39       39              
  Lines        8238     8235       -3     
  Branches     1442     1441       -1     
==========================================
- Hits         8012     8009       -3     
  Misses         98       98              
  Partials      128      128

Impacted Files	Coverage Δ
tests/autobahn/client.py	95.51% <0%> (-0.04%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 47188bb...bba8216. Read the comment docs.

[pfreixes]

Not sure if this MR is valid, I have to refresh my knowledge on Proxies but it smells weird to me. the Proxy authentication is done using an ad-hoc set of headers, more info here [1] [2]

[1] https://tools.ietf.org/html/rfc2617#page-19
[2] https://stackoverflow.com/questions/10023636/http-spec-proxy-authorization-and-authorization-headers

[asvetlov]

I don't understand what problem is fixed and what is the fix.
Moreover, code modification without adding/changing unit tests is not allowed.

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new