code: function loginUser(name, pass, cb) {
    // Get the user
    var db = nano().use(user_dbname)
    db.get(user_namespace+':'+name, function(err, doc) {
      if(err) return cb(err)
      
      // Check pass
      var hash = crypto.createHash('sha1')
      hash.update(pass)
      hash.update(doc.salt)
      var password_sha = hash.digest('hex')
      if(doc.password_sha === password_sha) {
        return cb(null, doc)
      }
      
      cb(new Error('Access denied.'))
    })
  }
docs: Checks loginUser credenciales