Why do I get a reference error even though I defined the function?

I have the following code that would execute, but on a button click that calls function 'Auth', I get an error that it is not defined. Why is that? I did define it in the below code, did I not?

app.get('/sign-in', function(req, res, next) {
  res.render('sign-in', {
    title: 'Sign In'
  })

  function Auth(event) {
    event.preventDefault()
    firebaseAuth.signInWithEmailAndPassword('email@email.com', 'password').catch(function(error) {
      var errorCode = error.code
      var errorMessage = error.message
      console.log(errorCode)
      console.log(errorMessage)
    })
  }
})

via kupak12