iPhone Calendar/ Contacts issue with self-signed certificate

[Jona]

I’ve just changed my certificate to a self-signed SSL. So far so good. Everything works fine for my mac, linux etc. But not with the Apple calendar and contacts app.
When I try to sync, the apps show some certificate not trusted despite having the cert added as trusted root certificate.

What I have done on the iPhone is:

1. download the PEM and install it.
2. under trusted certificates, (general, about, …) set this cert to on.

Weird thing is, that exactly the same certificate which is installed as trusted, later will be claimed by the calendar app.

Any ideas how to resolve this?

EDIT: Letsenrypt is not an option.

[Mornsgrans]

If your Nextcloud can be accessed from internet, get a free certificate from Letsencrypt.

[Bernie_O]

@Jona

I’ve just changed my certificate to a self-signed SSL

Does your self-signed certificate satisfy Apples requirements for trusted certificates?

[Jona]

Wow, thanks a lot. That was exactly the problem.
To all those people out there, who want to create a self-signed SSL certificate which works with iPhone and the rest of the world, use the following snippet:

  openssl req -x509 -newkey rsa:4096 -sha256 -days 365 \
  -nodes -keyout certname.key -out certname.crt -subj "/CN=domain.tld" \
  -addext "subjectAltName=DNS:domain.tld,DNS:*.domain.tld,IP:10.10.10.11"

Valid for 1 year, etc.