NegotiateStream.AuthenticateAsServerAsync Method (NetworkCredential, ProtectionLevel, TokenImpersonationLevel)

.NET Framework (current version)

Called by servers to authenticate the client, and optionally the server, in a client-server connection as an asynchronous operation. The authentication process uses the specified server credentials and authentication options.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)>
Public Overridable Function AuthenticateAsServerAsync (
	credential As NetworkCredential,
	requiredProtectionLevel As ProtectionLevel,
	requiredImpersonationLevel As TokenImpersonationLevel
) As Task


Type: System.Net.NetworkCredential

The NetworkCredential that is used to establish the identity of the server.

Type: System.Net.Security.ProtectionLevel

One of the ProtectionLevel values, indicating the security services for the stream.

Type: System.Security.Principal.TokenImpersonationLevel

One of the TokenImpersonationLevel values, indicating how the server can use the client's credentials to access resources.

Return Value

Type: System.Threading.Tasks.Task

Returns Task

The task object representing the asynchronous operation.

Exception Condition

credential is null.


requiredImpersonationLevel must be Identification, Impersonation, or Delegation,


The authentication failed. You can use this object to try to r-authenticate.


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 client. You cannot use the stream to retry authentication as the server.


Windows 95 and Windows 98 are not supported.

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.

.NET Framework
Available since 4.5
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