@nebulon thank you. I thought I tried LDAP but it works now. The trick is you need to click login after you click LDAP. Email address did not work for me. That may be because we do not use clouron for email.
This will be really hard for users since they need to learn to not use their email and to click the ldap button before the login button.
It would be very good if when the cloudron login is selected the option to login with email would not be shown and the LDAP was selected automatically.