// Delete the MFA Session Token with the given tokenId. Will only succeed
// if the user has MFA enabled and the token belongs to the user making the
// request.
public void DeleteMfaSessionToken(
    string username, 
    string password, 
    string apiKey,
    string tokenId)
{
    // Generate url and execute request with the XML payload we created earlier
    string url = "/Accounts/MfaSessionTokens/" + tokenId;
    MakeDeleteRequest(BaseUrl + url, username, password, apiKey);
}