bpo-39342: Expose X509_V_FLAG_ALLOW_PROXY_CERTS in ssl module (GH-18011)



Exposes the `X509_V_FLAG_ALLOW_PROXY_CERTS` constant as `ssl.VERIFY_ALLOW_PROXY_CERTS` to allow for proxy certificate validation as described in: https://www.openssl.org/docs/man1.1.1/man7/proxy-certificates.html
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 96d2796..bea144c 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -6181,6 +6181,8 @@ sslmodule_init_constants(PyObject *m)
                             X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
     PyModule_AddIntConstant(m, "VERIFY_X509_STRICT",
                             X509_V_FLAG_X509_STRICT);
+    PyModule_AddIntConstant(m, "VERIFY_ALLOW_PROXY_CERTS",
+                            X509_V_FLAG_ALLOW_PROXY_CERTS);
 #ifdef X509_V_FLAG_TRUSTED_FIRST
     PyModule_AddIntConstant(m, "VERIFY_X509_TRUSTED_FIRST",
                             X509_V_FLAG_TRUSTED_FIRST);