Sets the user name and password used to authenticate the feed.
HRESULT SetCredentials( BSTR username, BSTR password );
[in] BSTR that specifies the user name.
[in] BSTR that specifies the password.
Returns S_OK if successful, or an error value otherwise.
This method will set or update the user name and password stored in the credential manager for the feed.
User name and password are required. If either parameter is NULL or empty, the call will fail. To clear credentials, use IFeed::ClearCredentials.
Note Credentials are not removed when Internet Explorer 8 is uninstalled. They are removed when the feed is deleted.