Restore initial auth check endpoint

Might have been a little overzealous before... this endpoint does the initial auth/signup check for new users validating their email before being moved to the code login approach

Author: frederickobrien

app/src/routes/auth/confirm/+server.ts

@@ -0,0 +1,29 @@
+import type { EmailOtpType } from "@supabase/supabase-js";
+import { redirect, type RequestHandler } from "@sveltejs/kit";
+
+export const GET: RequestHandler = async ({ url, locals: { supabase } }) => {
+  const token_hash = url.searchParams.get("token_hash");
+  const type = url.searchParams.get("type") as EmailOtpType | null;
+  const next = url.searchParams.get("next") ?? "/";
+
+  /**
+   * Clean up the redirect URL by deleting the Auth flow parameters.
+   *
+   * `next` is preserved for now, because it's needed in the error case.
+   */
+  const redirectTo = new URL(url);
+  redirectTo.pathname = next;
+  redirectTo.searchParams.delete("token_hash");
+  redirectTo.searchParams.delete("type");
+
+  if (token_hash && type) {
+    const { error } = await supabase.auth.verifyOtp({ type, token_hash });
+    if (!error) {
+      redirectTo.searchParams.delete("next");
+      redirect(303, redirectTo);
+    }
+  }
+
+  redirectTo.pathname = "/auth/error";
+  redirect(303, redirectTo);
+};

app/src/routes/auth/error/+page.svelte

@@ -0,0 +1,2 @@
+<p>Login error</p>
+