"Username", "user name" or "user-name"

The OED gives ‘username’ and has three citations, from 1971, 1997 and 2007, in support.

The correct spelling in this case is username.

• The username is the (usually unique) thing you type in with your password, for example: bobsmith66.

• The user name is the name of the user, the user's real life name, for example: Bob Smith. User name is sometimes used for username, but occasionally it makes a difference, so be clear and avoid the ambiguity. (Better still, use full name when you want them to enter Bob Smith.)

• User-name is a variant of username, but this is rarely used if ever.

Obligatory Google Ngram:

In case the link breaks again: username is much more common these days; user-name is not used at all.

I've seen both "username" and "user name" used widely. Both are acceptable. As far as I know, techies mostly prefer "username". "User-name" just seems awkward.