Identify Mutual Authentication request at LDAPs

Question

Hello All,

We have a WPF application built on .Net Framework 4.8. This application acts as an LDAPs client for authentication purposes. The LDAPs server being used has provision for enabling mTLS.

When mTLS is enabled, the client application needs to send out the client certificate to LDAPs server.

When mTLS is disabled, the client application must not send out the client certificate to LDAPs server.

Currently, we are sending the client certificate every time irrespective of whether it was requested by the server or not.

But, we must be able to send the client certificate only when requested by LDAPs server. In other words, we must be able to know when the client certificate was requested by the server.

The question is how can this be achieved?

We have attached the code being used by us.LDAPs_Connection.txt

Can anyone please help us on this. Any help is appreciated!

Thank you in advance!!

Answer 1

Hi @S Abijith , Welcome to Microsoft Q&A,

System.DirectoryServices.Protocols.LdapConnection in .NET does not allow to directly check if the server has mTLS enabled.

If you have access to the LDAP server, you can check if mTLS is enabled by checking the server's configuration. Usually the server configuration file explicitly sets whether client certificate verification is enabled.

The only convenient way may be to use exception detection and send a test without a certificate before you send it. You can send the certificate after getting the target error.

If the server has mTLS enabled and the client does not provide a certificate, an exception will usually be thrown. You can infer whether mTLS is enabled by handling the exception. For example, when a client connects to an mTLS-enabled server and does not provide a certificate, an AuthenticationException or similar SSL error will usually be thrown.

try
{
ldapConnection.Bind(nc);
}
catch (AuthenticationException authEx)
{
// Catch TLS handshake failure, possibly because client certificate not provided
if (authEx.Message.Contains("required client certificate"))
{
// Server requires client certificate, mTLS may be enabled
Console.WriteLine("Server requires client certificate. mTLS may be enabled.");
}
else
{
// Other authentication issues
Console.WriteLine("Authentication failed: " + authEx.Message);
}
}

Best Regards,

Jiale

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Answer 2

To identify mutual authentication requests at LDAPs, it's crucial to understand the authentication flow. Mutual authentication ensures that both the client and server validate each other's identities. Start by examining the LDAP server logs for entries indicating secure connections, typically over LDAPS (LDAP over SSL). Look for successful bind operations that confirm mutual authentication, often accompanied by SSL handshake details. Additionally, utilize tools like Wireshark to monitor traffic and analyze the handshake process. By focusing on these elements, you can effectively identify and troubleshoot mutual authentication requests, ensuring a secure and reliable LDAP environment. Love Text Hubs