Update tls.md - Using Custom TLS Certificates

[abdounikarim]

Hello,

I just updated the docs using a custom TLS certificate.
When we don't specify the SERVER_NAME running just docker compose up --wait, the container is healthy but we have this error in docker logs:

php-1  | 2026/01/04 15:27:04.050	ERROR	The "MERCURE_TRANSPORT_URL"" environment variable is not supported anymore, set the "transport" directive in the "MERCURE_EXTRA_DIRECTIVES" environment variable instead

If we keep the 80 port in compose.yaml, we have this error:

php-1  | Error: adapting config using caddyfile: server listening on [:80] is HTTP, but attempts to configure TLS connection policies

If we remove the 80 port in compose.yaml, we have this error:

Error: adapting config using caddyfile: /etc/frankenphp/Caddyfile:19: parsed 'php' as a site address, but it is a known directive; directives must appear in a site block

By replacing the 80 port by 443 and using the SERVER_NAME=https://server-name.localhost docker compose up --wait everything seems to work.

Reproducer:

1. Create a brand fresh new project
2. Follow the tls.md docs using a custom certificate

WDYT ?

[7-zete-7]

Hi @abdounikarim!

ERROR The "MERCURE_TRANSPORT_URL"" environment variable is not supported anymore <…>

This is a Mercure configuration error. Changing SERVER_NAME shouldn't cause it. A related issue is discussed here and here. The error itself only informs you that the configuration is being ignored and Mercure will use the default settings (see dunglas/mercure#1129).

---

I guess the php:80 host will soon be unnecessary since the mercure_publish() function has been added to FrankenPHP (see https://frankenphp.dev/docs/mercure/#publishing-updates). After removing this host, there should be no problems with configuring TLS according to the documentation.