url: detect proxy changes read from environment

[bagder]

No description provided.

[testclutch]

Analysis of PR #21666 at a8605a04:

Test 3207 failed, but it has been 1.4% flaky lately, so it's probably NOT a fault of the PR. Note that this test has failed in 4 different CI jobs (the link just goes to one of them). Note that this CI job has had a number of other flaky tests recently (3, to be exact) so it may be that this failure is rather a systemic issue with this job and not with this specific PR.

Generated by Testclutch

[Copilot]

Pull request overview

This PR adds tracking for proxy changes (notably those coming from environment proxy detection) so libcurl can reset proxy Digest auth state when the proxy changes between transfers on the same easy handle. It also introduces a new libtest-based regression test case to exercise this behavior.

Changes:

• Track the last-used proxy string in UrlState and clear state.proxydigest when the proxy changes.
• Add new libtest lib1630 plus test spec test1630 to validate proxy change handling across two transfers.
• Wire the new test into the test build system.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tests/libtest/Makefile.inc	Adds lib1630.c to the libtest build.
tests/libtest/lib1630.c	New libtest that performs two transfers relying on env proxies and proxy Digest auth.
tests/data/test1630	New test definition for the regression scenario.
tests/data/Makefile.am	Adds the new test case to the test list (currently duplicated).
lib/urldata.h	Adds UrlState.envproxy to track last proxy string.
lib/url.c	Frees envproxy on cleanup and clears proxy Digest state when proxy changes.

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[bagder]

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[augmentcode]

🤖 Augment PR Summary

Summary: This PR makes libcurl detect when the effective proxy (as resolved from environment variables) changes between transfers, and resets proxy Digest auth state accordingly.

Changes:

• Track the last proxy string used in a new UrlState.envproxy field.
• In url_set_conn_proxies(), compare the current proxy string against the cached one and, when it changes, clear the cached proxy Digest auth data (proxydigest).
• Free the cached proxy string during Curl_close() cleanup.
• Add a new regression test (test1647 + lib1647.c) that first authenticates to an HTTP proxy with Digest, then switches proxies via env vars and verifies state is not reused.
• Update test Makefiles to include the new test case and libtest source.

Technical Notes: The intent appears to be preventing proxy Digest state (nonce/realm/etc) from being reused after the proxy endpoint changes, which could otherwise cause incorrect/unsafe preemptive auth behavior.

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