Show error page if ask directive of on_demand_tls fails

[abishekrsrikaanth]

1. The problem I’m having:

I am using the ask directive of on_demand_tls. If a particular domain doesn’t exist, right now it shows “url sent an invalid response, ERR_SSL_PROTOCOL_ERROR”. Is there a way to show a html page instead of this?

2. Error messages and/or full log output:

NA

3. Caddy version:

v2.6.4

Install - Caddy Documentation

a. System environment:

Ubuntu 22.04

b. Command:

NA

c. Service/unit/compose file:

NA

d. My complete Caddy config:

NA

5. Links to relevant resources:

NA

[francislavoie]

That’s impossible. If the TLS handshake fails, the client can’t trust anything coming from the server, so you’ll only ever be able to see the browser’s own error messages.

[matt (Matt Holt)]

And to be clear, this is just how the Web works – not a limitation of Caddy, per-se. Browsers won’t even establish a secure connection without a valid certificate, so there’s no way to send an HTML response back.