On Debian you'll probably want to
apt install nslcd and configure it with your LDAP details (or
dpkg-reconfigure nslcd if already installed), then install/(re)configure libnss-ldapd for including the LDAP data into the name database and finally libpam-ldapd to enable the PAM LDAP module, if you use PAM for authorization. Equivalently, edit
/etc/nslcd.conf (then reload nslcd),
/etc/pam.d/common-auth (or some other service file if you don't need generic coverage across all PAM services). See also
man pam-auth-update in case the defaults don't fit you.
Once the above works, consider
apt install unscd for better performance, but don't forget that this cache will have only delayed consistency with your LDAP database.