Redirect callback example in docs - reversed logic in ternary

[jacobedawson]

I was struggling with getting a signIn / signOut redirect callback working. After checking the docs, specifically the Redirect Callback example at https://next-auth.js.org/configuration/callbacks I was not seeing the behaviour I expected (which was to redirect the user to /dashboard on login, and to / on logout).

It appears that the example in the docs is back to front:

  redirect: async (url, baseUrl) => {
    return url.startsWith(baseUrl)
      ? Promise.resolve(url)
      : Promise.resolve(baseUrl)
  }

Should be

  redirect: async (url, baseUrl) => {
    return url.startsWith(baseUrl)
      ? Promise.resolve(baseUrl)
      : Promise.resolve(url)
  }

In the redirect method in the [...nextauth] file, the function signature takes url, baseUrl. In the signIn method we can pass options including callbackUrl, which will appear as the first argument (url) in the redirect method.

So when I pass the following to signIn and log url, baseUrl:

signIn(provider.id, {
  callbackUrl: "/dashboard"
})

/dashboard will be the first argument, and that is where I would like the user to be redirected after signIn. By swapping the order in the ternary statement the signIn / signOut redirects work as expected. When using the ternary example in the docs the signIn / signOut redirects do not work as expected (or at least not intuitively).

It's very late and I'm tired so I could be wrong, so I want to add this as a bug first, and if I'm not mistaken then I can make a pull request to update the docs. If I am mistaken, I may make a pull request to add clarity to the docs regarding signIn / signOut redirects, since imo it isn't very clear (and I have noticed a fair few questions regarding auth redirects in the issues).

[balazsorban44]

Hi there! The docs says:

By default only URLs on the same URL as the site are allowed, you can use the redirect callback to customise that behaviour.

Meaning that by default, only absolute URLs are handled, that also match (starts with) the base url , all others will go to the baeUrl or the homepage.

To support relative urls, this is what I did in our app:

async redirect(url, baseUrl) {
  if(url.startsWith(baseUrl) {
    return url
  }

  return new URL(url, baseUrl).toString()
}