Steam's approach to authentication is annoying. You either get their authenticator app for two-factor authentication, or get demoted to a second-class Steam citizen. Without the authenticator you get nagged frequently to get it, and you cannot buy and sell things on the marketplace normally (every action has to be confirmed via email, and any item you want to sell is placed in escrow for
two weeks).
I appreciate Valve pushing for better security, but with the authenticator app the only option this really sucks if you don't have a smartphone, or do have a smartphone, just not with Android, IOS, or Windows Phone on it.
Now I understand this for the interim (people were losing their digital items due to poor security), but it is damn near impossible to contact Steam with suggestions or comments (on the Steam forums your voice is drowned in a sea of despair, and I can't seem to get a hold of anyone with a technical background at Steam's help-desk). Perhaps if someone at Valve is reading HN: please consider using Fido U2F as an alternative to a smartphone app!