HTTPRedirectHandler fails on POST for 307 and 308

[Yajo]

BPO	47150
Nosy	@orsenthil, @corona10, @yajo

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-03-29.09:26:11.943>
labels = ['type-bug', '3.8', '3.9', '3.10', '3.11', 'library']
title = 'HTTPRedirectHandler fails on POST for 307 and 308'
updated_at = <Date 2022-03-31.00:07:30.666>
user = 'https://github.com/Yajo'

bugs.python.org fields:

activity = <Date 2022-03-31.00:07:30.666>
actor = 'ned.deily'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2022-03-29.09:26:11.943>
creator = 'Jairo Llopis'
dependencies = []
files = []
hgrepos = []
issue_num = 47150
keywords = []
message_count = 1.0
messages = ['416249']
nosy_count = 3.0
nosy_names = ['orsenthil', 'corona10', 'Jairo Llopis']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue47150'
versions = ['Python 3.8', 'Python 3.9', 'Python 3.10', 'Python 3.11']

[Yajo]

urllib.request.HTTPRedirectHandler fails if there is a 307 HTTP return code in a POST request.

In c379bc5 the same behaviour was implemented for 308.

According to https://datatracker.ietf.org/doc/html/rfc7538#section-3 IMHO this implementation is wrong for 308:

Note: This status code is similar to 301 (Moved Permanently)
([RFC7231], Section 6.4.2), except that it does not allow changing
the request method from POST to GET.

A similar note exists in https://datatracker.ietf.org/doc/html/rfc7231#section-6.4.7 regarding code 307.

So, as long as the original redirection is in POST and it gets redirected to another POST, it should not be an error.

FWIW, in traefik/traefik#7829 (comment) you can see that Traefik proxy uses 307 and 308 codes by default when redirecting non-GET requests.

Thus, urllib.request.HTTPRedirectHandler will fail to process any POST requests proxied by Traefik.