HttpWebRequest.ClientCertificates Property

Gets or sets the collection of security certificates that are associated with this request.

Namespace: System.Net
Assembly: System (in system.dll)

public X509CertificateCollection ClientCertificates { get; set; }
/** @property */
public X509CertificateCollection get_ClientCertificates ()

/** @property */
public void set_ClientCertificates (X509CertificateCollection value)

public function get ClientCertificates () : X509CertificateCollection

public function set ClientCertificates (value : X509CertificateCollection)

Not applicable.

Property Value

The X509CertificateCollection that contains the security certificates associated with this request.

Exception typeCondition


The value specified for a set operation is a null reference (Nothing in Visual Basic).

An application can add a certificate to a collection, but might not have access rights to it. To use a certificate contained in the collection, the application must have the same access rights as the entity that issued the certificate.


The Framework caches SSL sessions as they are created and attempts to reuse a cached session for a new request, if possible. When attempting to reuse an SSL session, the Framework uses the first element of ClientCertificates (if there is one), or tries to reuse an anonymous sessions if ClientCertificates is empty.


For performance reasons, you shouldn't add a client certificate to a HttpWebRequest unless you know the server will ask for it.

For a code example illustrating how to enumerate the certificates in the client certificate store, see the X509Certificate2Collection class.

Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition Platform Note: The Framework attempts to reuse an SSL session only if a client certificate is not required.

Windows Mobile 2003 for Pocket PC, Windows Mobile 2003 for Smartphone, Windows CE Platform Note: Only the first client certificate from the client certificate collection will be sent during the client authentication phase, regardless of the list of trusted CAs from the server. This limitation will be corrected in a future release of the .NET Compact Framework.

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0