Assembly: Microsoft.Office.Server.Search (in microsoft.office.server.search.dll)
There are two classes that you can use to represent forms authentication data for federated search locations:
FormsAuthCredentials: Use this class when you programmatically configure federated locations.
FormsCredentials: Use this class in custom federated results Web Parts, when specifying credentials for federated locations that are configured for per user cookie-based authentication. For more information, see Creating a Custom Federated Search Web Part with a Credentials UI.