Implement verify server cert on linux

[JasonDebug]

In an attempt to address #60972, I've implemented VerifyServerCertificate for Linux using OpenSSL and OpenLDAP. I have confirmed via network trace that returning false from the callback will sever the connection with a RST on the wire.

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[Copilot]

Pull request overview

Adds Linux support for LdapSessionOptions.VerifyServerCertificate by wiring OpenLDAP’s TLS connect hook to an OpenSSL verify callback, aligning behavior more closely with the existing Windows implementation and addressing #60972.

Changes:

• Refactors VerifyServerCertificate/callback plumbing into OS-specific partials and initializes the callback delegate per-platform.
• Implements Linux TLS server-certificate verification via OpenLDAP LDAP_OPT_X_TLS_CONNECT_CB + OpenSSL SSL_set_verify.
• Introduces new OpenLDAP/OpenSSL interop declarations and adds the OpenSSL interop file to the build.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/ldap/LdapSessionOptions.cs	Moves server-cert verification wiring out to OS partials; calls per-OS initializer.
src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/ldap/LdapSessionOptions.Windows.cs	Restores Windows VerifyServerCertificate property and callback implementation.
src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/ldap/LdapSessionOptions.Linux.cs	Implements Linux VerifyServerCertificate using OpenLDAP TLS connect callback + OpenSSL verify callback.
src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/Interop/LdapPal.Linux.cs	Adjusts Linux PAL server-cert option setter to accept an IntPtr.
src/libraries/System.DirectoryServices.Protocols/src/System.DirectoryServices.Protocols.csproj	Includes the new OpenSSL interop file for linux/osx builds.
src/libraries/Common/src/Interop/Windows/Wldap32/Interop.Ldap.cs	Relocates VERIFYSERVERCERT delegate definition into Windows interop.
src/libraries/Common/src/Interop/Linux/OpenSsl/Interop.OpenSsl.cs	Adds OpenSSL P/Invokes for verify callback support.
src/libraries/Common/src/Interop/Linux/OpenLdap/Interop.Ldap.cs	Adds TLS connect callback delegate and a pointer-valued ldap_set_option P/Invoke.
src/libraries/Common/src/Interop/Interop.Ldap.cs	Adds OpenLDAP TLS connect option enum values.

Comments suppressed due to low confidence (2)

src/libraries/System.DirectoryServices.Protocols/src/System/DirectoryServices/Protocols/ldap/LdapSessionOptions.Linux.cs:194

• The new VerifyServerCertificate implementation on Linux bypasses the PAL layer and calls Interop.Ldap.ldap_set_option_ptr_value directly. Please consider adding a dedicated LdapPal helper for setting the TLS connect callback (and using it here) to keep interop usage centralized and consistent with other options.

                if (value != null)
                {
                    IntPtr functionPointer = Marshal.GetFunctionPointerForDelegate(_serverCertificateRoutine);
                    int error = Interop.Ldap.ldap_set_option_ptr_value(_connection._ldapHandle, LdapOption.LDAP_OPT_X_TLS_CONNECT_CB, functionPointer);

                    ErrorChecking.CheckAndSetLdapError(error);
                }

src/libraries/Common/src/Interop/Linux/OpenLdap/Interop.Ldap.cs:170

• The ldap_set_option_ptr_value addition leaves behind commented-out P/Invoke declarations. Please remove the commented code to keep the interop surface clean and avoid confusion about which signature is correct.

        //[LibraryImport(Libraries.OpenLdap, EntryPoint = "ldap_set_option")]
        //public static partial int ldap_set_option_ptr(IntPtr ldapHandle, LdapOption option, ref IntPtr inValue);

[Copilot]

cert.Dispose() in the verify callback can leave user code holding a disposed X509Certificate instance if they capture it from the callback for later inspection/logging. Windows implementation doesn’t dispose the certificate passed to the delegate. To keep behavior consistent and avoid surprising ObjectDisposedExceptions, don’t dispose the certificate here (or pass a non-disposable clone).

Suggested change

cert.Dispose();

[Copilot]

LdapPal.SetServerCertOption now wraps ldap_set_option_ptr with a ref IntPtr, which passes a pointer-to-pointer. For options like LDAP_OPT_X_TLS_CONNECT_CB (function pointer value), the call sites in this PR use a different P/Invoke that passes the pointer value directly. To prevent future misuse, either remove SetServerCertOption on Linux if it’s unused, or implement it in terms of the correct setter (ldap_set_option_ptr_value) for callback-style options.

Suggested change

	internal static int SetServerCertOption(ConnectionHandle ldapHandle, LdapOption option, IntPtr inValue)
	{
	IntPtr functionPointer = inValue;
	return Interop.Ldap.ldap_set_option_ptr(ldapHandle, option, ref functionPointer);
	}
	internal static int SetServerCertOption(ConnectionHandle ldapHandle, LdapOption option, IntPtr inValue) =>
	Interop.Ldap.ldap_set_option_ptr_value(ldapHandle, option, inValue);

[Copilot]

With Linux support added, VerifyServerCertificate is no longer Windows-only behavior, but existing tests currently validate set/get only on Windows. Please extend LdapSessionOptionsTests.VerifyServerCertificate_Set_GetReturnsExpected to run on Linux as well (and ideally validate that returning false aborts the handshake, if test infrastructure allows).

Suggested change

	if (value != null)
	{
	IntPtr functionPointer = Marshal.GetFunctionPointerForDelegate(_serverCertificateRoutine);
	int error = Interop.Ldap.ldap_set_option_ptr_value(_connection._ldapHandle, LdapOption.LDAP_OPT_X_TLS_CONNECT_CB, functionPointer);
	ErrorChecking.CheckAndSetLdapError(error);
	}
	IntPtr functionPointer = value is not null
	? Marshal.GetFunctionPointerForDelegate(_serverCertificateRoutine)
	: IntPtr.Zero;
	int error = Interop.Ldap.ldap_set_option_ptr_value(
	_connection._ldapHandle,
	LdapOption.LDAP_OPT_X_TLS_CONNECT_CB,
	functionPointer);
	ErrorChecking.CheckAndSetLdapError(error);

[Copilot]

Interop.OpenSsl hardcodes libssl.so.3/libcrypto.so.3, which will fail on supported distros that still ship OpenSSL 1.1 (and it also won’t work on macOS). Please switch to a version-resilient loading strategy consistent with the repo (e.g., route through the existing OpenSSL shim in System.Security.Cryptography.Native, or introduce a shim export for the needed APIs) rather than binding directly to versioned .so names.

Suggested change

	private const string LibSsl = "libssl.so.3";
	private const string LibCrypto = "libcrypto.so.3";
	private const string LibSsl = "libssl";
	private const string LibCrypto = "libcrypto";

[Copilot]

This new OpenSSL interop file is added to the linux or osx compile ItemGroup, but it P/Invokes Linux .so names. That means setting VerifyServerCertificate on macOS will likely throw DllNotFoundException. If the intent is Linux-only support, restrict inclusion to Linux; otherwise add an OS X-specific interop (or a shared shim-based approach) that resolves the correct library names.

[Copilot]

_verifyCallbackInvoked/_verifyCallbackResult are only initialized in the constructor. If the same LdapConnection performs more than one TLS handshake over its lifetime (reconnect, StartTLS again, etc.), the callback result from the first handshake will be reused and the user delegate won’t run again. Consider resetting this per-handshake (e.g., when SetOpenSslCallback is invoked) rather than per LdapSessionOptions instance.