Gets the last instant in time at which this security token is valid.
Assembly: System.IdentityModel (in System.IdentityModel.dll)
Use the ValidFrom and properties to determine the time period in which a GenericXmlSecurityToken token is valid. The ValidFrom and properties represent the first and last instants in time in which the security token is valid, respectively.
The property is specified using the expirationTime parameter of the constructor. The value returned from this property is always in Coordinated Universal Time (UTC).