[WIP] Sign-in-or-up docs

[alexcarpenter]

Important

🔎 Previews:

• https://clerk.com/docs/pr/1772/references/nextjs/custom-sign-in-or-up-page
• https://clerk.com/docs/pr/1772/references/nextjs/custom-signup-page
• https://clerk.com/docs/pr/1772/customization/account-portal/overview

Explanation:

Resolves SDKI-747

We are introducing a combined sign-in-or-up flow that will be the default experience using the <SignIn /> component. Users will be able to still opt-in to a custom <SignUp /> page by adding a custom sign-up route along with setting their CLERK_SIGN_UP_URL.

This update will also default Account Portal to using the combined flow, instead of having separate sign-in sign-up pages.

This PR:

• Introduce documentation on combined sign-in-or-up flows using <SignIn /> component
• Introduce redirect https://github.com/clerk/clerk/pull/853

  {
    "source": "/docs/references/:path/custom-signup-signin-pages",
    "destination": "/docs/references/:path/custom-sign-in-or-up-page",
    "permanent": true,
  },

Checklist

• I have clicked on "Files changed" and performed a thorough self-review
• I have added the "deploy-preview" label and added the preview link(s) to this PR description
• All existing checks pass

[github-actions]

Hey, here’s your docs preview: https://clerk.com/docs/pr/1772