Active Directory integration doesn't work with SSL and port 636

    Windows: c:\openldap\sysconf\ldap.conf
    Ubuntu: /etc/ldap/ldap.conf 
    RHEL: /etc/openldap/ldap.conf

2.  Add the following lines to the ldap.conf file based on how the AD server 

     If your AD server doesn't have an SSL installed and SSL verification is not needed the contents in the file should be:

     TLS_REQCERT never

     If your AD server have an SSL installed and SSL verification is needed the contents in the file should be:

      TLS_REQCERT allow
      TLS_CACERT c:\openldap\sysconf\certs\CACERT_NAME
      TLS_CACERTDIR c:\openldap\sysconf\certs

      or

      TLS_REQCERT allow
      TLS_CACERTDIR c:\openldap\sysconf\certs
      
      Here, CACERT_NAME is the name of your CA certificate imported from AD and the certificates should be placed under c:\openldap\sysconf\certs

      If your AD server have an SSL installed and SSL verification is needed along with strict Cipher check the contents in the file should be:

      TLS_REQCERT allow
      TLS_CACERT c:\openldap\sysconf\certs\CACERT_NAME
      TLS_CACERTDIR c:\openldap\sysconf\certs
      SSLCipherSuite AES256-GCM-SHA384:AES256-AES256:AES256-SHA

      Here, Cipher value can be changed as per your setup.

3. Restart Apache and check the Active Directory connection