If it's plain OpenLDAP
The libpam-ldapd route is the least painful because the installer prompts you interactively and auto-configures nsswitch.conf + PAM:

sudo apt install libnss-ldapd libpam-ldapd

When it prompts, just fill in:

LDAP server URI: ldap://your-server:389
Search base: dc=example,dc=com
Check passwd, group, shadow 
Then set the bind DN/password:

sudo nano /etc/nslcd.conf

binddn "cn=readonly,dc=example,dc=com"
bindpw your-password

sudo systemctl restart nslcd
sudo reboot


# /etc/nslcd.conf
# nslcd configuration file. See nslcd.conf(5)
# for details.

# The user and group nslcd should run as.
uid nslcd
gid nslcd

# The location at which the LDAP server(s) should be reachable.
uri ldap://10.3.12.13:3189

# The search base that will be used for all queries.
base dc=rhodiumlab,dc=org

# The LDAP protocol version to use.
#ldap_version 3

# The DN to bind with for normal lookups.
binddn cn=admin,dc=rhodiumlab,dc=org
bindpw "password"

# The DN used for password modifications by root.
#rootpwmoddn cn=admin,dc=example,dc=com

# SSL options
#ssl off
#tls_reqcert never
tls_cacertfile /etc/ssl/certs/ca-certificates.crt

# The search scope.
#scope sub