protected override IAsyncResult OnBeginGetToken(string appliesTo, string action, TimeSpan timeout, AsyncCallback callback, object state)
        {
            base.ValidateAction(action);
            Uri stsUri = TokenProviderHelper.GetStsUri(this.stsUri, appliesTo);

            TokenProviderHelper.TokenResult <SecurityToken> accessTokenByAssertion = TokenProviderHelper.GetAccessTokenByAssertion(stsUri, appliesTo, this.SimpleWebToken, "SWT", timeout);
            return(new CompletedAsyncResult <TokenProviderHelper.TokenResult <SecurityToken> >(accessTokenByAssertion, callback, state));
        }