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/Doc/library/ssl.rst b/Doc/library/ssl.rst
index 1cfd165..1adac84 100644
--- a/Doc/library/ssl.rst
+++ b/Doc/library/ssl.rst
@@ -634,6 +634,13 @@
 
    .. versionadded:: 3.4
 
+.. data:: VERIFY_ALLOW_PROXY_CERTS
+
+   Possible value for :attr:`SSLContext.verify_flags` to enables proxy
+   certificate verification.
+
+   .. versionadded:: 3.10
+
 .. data:: VERIFY_X509_TRUSTED_FIRST
 
    Possible value for :attr:`SSLContext.verify_flags`. It instructs OpenSSL to