Keycloak as replacment for ldap to provide identity and authentication for Nextcloud, postfix, dovecot

Hi There,

I’m setting up a Nextcloud instance with mail possibilities for a group les than 30 persons.
On my vps I have running Nextcloud, Postfix, Postfixadmin, Dovecot, Keycloak and Wordpress.
This all runs fine, however when users changes their password in Keycloak. Postfixadmin isn’t aware of this change and hence the mail stops functioning in Nextcloud.
I read about solutions of using ldap, however I didn’t find a understandable explanation for me why ldap would be able to be the identity provider for all these apps but Keycloak not.
Openldap or apacheds seems to be 2 valid choices but as I’m using a vps I need to manage this remotely. Preferably with a web ui.

How is what I want to do normally done?
Thanks for reading