I don't like the old style NSDictionary way of packing information that so many API's use. First of all they're lacking an enforcement for the type of the value they're expecting (sometimes leading to crashes if you get them wrong) and the discoverability of possibilities is less easy than with a struct or object.

Still, passing in password twice would still be a possible mistake. The only thing that would help in my opinion would be types that can be applied to primitives, a bit like F# does. So you can declare certain Doubles to be Miles, Kilometers, Meters and so on. Or a certain type of string can be of type DatabaseID or a Password.