Where the **** do I enter the verification code?

When I'm trying to logon from my desktop, I get a message on my iPhone, asking me to allow the logon. It then gives me a verification code, and tells me to enter it on the logon page. But there's no place on the logon page for the verification code! I tried putting it it before and after my password, and was told both times that the password was incorrect. Possibly this is rank stupidity on my part, but it isn't really intuitive to me.