AuthenticateAsClientAsync Method

NegotiateStream.AuthenticateAsClientAsync Method ()

.NET Framework 4.6 and 4.5

Called by clients to authenticate the client, and optionally the server, in a client-server connection as an asynchronous operation.

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

[HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading = true)]
public virtual Task AuthenticateAsClientAsync()

Return Value

Type: System.Threading.Tasks.Task

Returns Task

The task object representing the asynchronous operation.

Exception Condition

The authentication failed. You can use this object to retry the authentication.


The authentication failed. You can use this object to retry the authentication.


This object has been closed.


Authentication has already occurred.

- or -

This stream was used previously to attempt authentication as the server. You cannot use the stream to retry authentication as the client.

The authentication uses the client's DefaultCredentials. No Service Principal Name (SPN) is specified for the server. The impersonation level is Identification, the security level is EncryptAndSign, and mutual authentication is requested. The NegotiateStream class will construct the SPN used for mutual authentication.

When authentication succeeds, you must check the IsEncrypted and IsSigned properties to determine what security services are used by the NegotiateStream. Check the IsMutuallyAuthenticated property to determine whether mutual authentication occurred.

If the authentication fails, you receive an AuthenticationException or an InvalidCredentialException. In this case, you can retry the authentication with a different credential.


to use the explicit System.Net.NetworkCredential. Associated enumeration: SecurityPermissionFlag.ControlPrincipal.

.NET Framework
Available since 4.5
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