Super basic authentication example

auth.js

const users = [
  {
    username: 'foo',
    password: 'bar'
  }
]

const authenticate = credentials => {
  if (!credentials || !credentials.username || !credentials.password) {
    // credentials were not passed in
    return false
  }

  const user = users.find(u => u.username === credentials.username)

  if (!user) {
    // user doesn't exist
    return false
  }

  if (credentials.password !== user.password) {
    // user exists but password didn't match
    return false
  }

  // user exists and password matched
  return true
}

// wrong password
authenticate({
  username: 'foo',
  password: 'wrong'
})
// false

// wrong username
authenticate({
  username: 'wrong',
  password: 'bar'
})
// false

//both correct
authenticate({
  username: 'foo',
  password: 'bar'
})
// true