Pass HTTPS and client TLS certificates to build subprocesses

The _PIP_STANDALONE_CERT environment variable hack is no longer required
as pip doesn't run a zip archive of itself to provision build
dependencies these days (which due to a CPython bug would leave behind
temporary certifi files).

news/5502.bugfix.rst

@@ -0,0 +1 @@
+Configured TLS server and client certificates are now used while installing build dependencies.

src/pip/_internal/build_env.py

@@ -246,6 +246,8 @@ def _install_requirements(
             # target from config file or env var should be ignored
             "--target",
             "",
+            "--cert",
+            finder.custom_cert or where(),
         ]
         if logger.getEffectiveLevel() <= logging.DEBUG:
             args.append("-vv")
@@ -272,19 +274,19 @@ def _install_requirements(
 
         for host in finder.trusted_hosts:
             args.extend(["--trusted-host", host])
+        if finder.client_cert:
+            args.extend(["--client-cert", finder.client_cert])
         if finder.allow_all_prereleases:
             args.append("--pre")
         if finder.prefer_binary:
             args.append("--prefer-binary")
         args.append("--")
         args.extend(requirements)
-        extra_environ = {"_PIP_STANDALONE_CERT": where()}
         with open_spinner(f"Installing {kind}") as spinner:
             call_subprocess(
                 args,
                 command_desc=f"pip subprocess to install {kind}",
                 spinner=spinner,
-                extra_environ=extra_environ,
             )
 
 

src/pip/_internal/index/package_finder.py

@@ -680,6 +680,20 @@ def trusted_hosts(self) -> Iterable[str]:
         for host_port in self._link_collector.session.pip_trusted_origins:
             yield build_netloc(*host_port)
 
+    @property
+    def custom_cert(self) -> Optional[str]:
+        # session.verify is either a boolean (use default bundle/no SSL
+        # verification) or a string path to a custom CA bundle to use. We only
+        # care about the latter.
+        verify = self._link_collector.session.verify
+        return verify if isinstance(verify, str) else None
+
+    @property
+    def client_cert(self) -> Optional[str]:
+        cert = self._link_collector.session.cert
+        assert not isinstance(cert, tuple), "pip only supports PEM client certs"
+        return cert
+
     @property
     def allow_all_prereleases(self) -> bool:
         return self._candidate_prefs.allow_all_prereleases

src/pip/_vendor/requests/certs.py

@@ -11,14 +11,7 @@
 environment, you can change the definition of where() to return a separately
 packaged CA bundle.
 """
-
-import os
-
-if "_PIP_STANDALONE_CERT" not in os.environ:
-    from pip._vendor.certifi import where
-else:
-    def where():
-        return os.environ["_PIP_STANDALONE_CERT"]
+from pip._vendor.certifi import where
 
 if __name__ == "__main__":
     print(where())

tests/functional/test_install.py

@@ -2361,6 +2361,38 @@ def test_install_sends_client_cert(
         assert environ["SSL_CLIENT_CERT"]
 
 
+def test_install_sends_certs_for_pep518_deps(
+    script: PipTestEnvironment,
+    cert_factory: CertFactory,
+    data: TestData,
+    common_wheels: Path,
+) -> None:
+    cert_path = cert_factory()
+    ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
+    ctx.load_cert_chain(cert_path, cert_path)
+    ctx.load_verify_locations(cafile=cert_path)
+    ctx.verify_mode = ssl.CERT_REQUIRED
+
+    setuptools_pkg = next(common_wheels.glob("setuptools*")).name
+    server = make_mock_server(ssl_context=ctx)
+    server.mock.side_effect = [
+        package_page({setuptools_pkg: f"/files/{setuptools_pkg}"}),
+        file_response(common_wheels / setuptools_pkg),
+    ]
+    url = f"https://{server.host}:{server.port}/simple"
+
+    args = ["install", str(data.packages / "pep517_setup_and_pyproject")]
+    args.extend(["--index-url", url])
+    args.extend(["--cert", cert_path, "--client-cert", cert_path])
+
+    with server_running(server):
+        script.pip(*args)
+
+    for call_args in server.mock.call_args_list:
+        environ, _ = call_args.args
+        assert environ.get("SSL_CLIENT_CERT", "")
+
+
 def test_install_skip_work_dir_pkg(script: PipTestEnvironment, data: TestData) -> None:
     """
     Test that install of a package in working directory

tools/vendoring/patches/requests.patch

@@ -84,26 +84,6 @@ index 8fbcd656..094e2046 100644
 
  try:
      from urllib3.contrib import pyopenssl
-diff --git a/src/pip/_vendor/requests/certs.py b/src/pip/_vendor/requests/certs.py
-index be422c3e..3daf06f6 100644
---- a/src/pip/_vendor/requests/certs.py
-+++ b/src/pip/_vendor/requests/certs.py
-@@ -11,7 +11,14 @@ If you are packaging Requests, e.g., for a Linux distribution or a managed
- environment, you can change the definition of where() to return a separately
- packaged CA bundle.
- """
--from certifi import where
-+
-+import os
-+
-+if "_PIP_STANDALONE_CERT" not in os.environ:
-+    from certifi import where
-+else:
-+    def where():
-+        return os.environ["_PIP_STANDALONE_CERT"]
-
- if __name__ == "__main__":
-     print(where())
 diff --git a/src/pip/_vendor/requests/__init__.py b/src/pip/_vendor/requests/__init__.py
 index 9d4e72c60..04230fc8d 100644
 --- a/src/pip/_vendor/requests/__init__.py