After upgrading a CQ5.2.1 authoring instance to 5.3 we are unable to login.
You would experience this issue only if you have customized the CQ5.2.X login page.
Where a custom login page at /apps/wcm/auth/content/login is used, it needs to be adapted as follows:
- Change the sling:resourceType property of the login node from wcm/auth/components/login to cq/core/components/login
- move all the static files (background image, css and js) below the /apps/wcm/auth/content/login node