Example: At each startup a new row for the user is add to the database

[johnny324]

This leads to an error which is not caught when running
err := dbmap.SelectOne(&user, "SELECT * FROM users WHERE username = $1 and password = $2", postedUser.Username, postedUser.Password)

I'd suggest to put in after the db connection has been opened
db.Exec("DROP TABLE IF EXISTS users;")