FusionAuth supports customization for some of these scenarios through themes, but not all:
1. Root Path Customization
This is possible. The Index page can be customized through your FusionAuth theme. You can add a redirect (for example, using JavaScript or a meta refresh tag) to send users to your application's login page.
Important: When FusionAuth can't identify the tenant (including when browsing to / without client_id or tenantId parameters), it uses the default tenant. To theme the root page:
Create a copy of the built-in theme — the default theme is immutable because it ships with FusionAuth
Edit the index template in your copy to include your redirect (using JavaScript like window.location.href = "https://yourapp.com/login" or HTML meta refresh)
Apply this theme to ALL tenants, including the default tenant
Test with tenant specified — try the root URL with tenantId or client_id to confirm your edited theme renders
See the Advanced Themes troubleshooting guide for more details on theme issues.
Related: GitHub Issue #378
2. OAuth Error Handling
This is also possible. The OAuth error page can be customized in your theme, so you can implement the same redirect approach for customers who saved stale or broken login links. The OAuth error template is available for customization and you can add JavaScript or meta refresh redirects to handle these scenarios.
Note that OAuth errors can also be returned as redirect parameters to your application's callback URL (depending on the OAuth flow), which allows your application to handle errors directly rather than showing the FusionAuth-hosted error page.
3. 404 Pages for Invalid URLs
This is NOT currently customizable. The 404 page cannot be customized, including on Cloud deployments. Requests to invalid paths (like /whatever) will show the default error page. This is a known limitation tracked in GitHub Issue #404, which requests additional themed error pages (including 404 and 500 pages).
Summary
You can handle root path and OAuth error redirects through theme customization by adding JavaScript redirects to the index and OAuth error templates. However, true 404 pages remain uncustomizable. CloudFront configuration is not exposed to customers on cloud deployments, so there's no workaround at that layer.
Related Documentation
Advanced Themes Documentation - Complete guide to customizing FusionAuth themes
Theme Templates - Full list of available templates including Index and OAuth error
Theme Template Variables - Variables available in each template
Index Template Variables - Specific to the root page
OAuth Error Template Variables - Specific to OAuth error page
OAuth Error API Documentation - How OAuth errors are returned
Default Tenant Configuration - Understanding the default tenant