Nextcloud version: 19.0.1
Operating system and version: Ubuntu 20.04
Apache or nginx version: Apache/2.4.41 (Ubuntu)
PHP version: 7.4
The issue you are facing:
Nextcloud log throws below error message, however ldap auth is working. But I dont like errors in my logs 
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
- don’t know
The output of your Nextcloud log in Admin > Logging:
Error user_ldap Attempt for Paging? 1 2020-07-21T13:55:01+0200
Error PHP ldap_search(): Search: Critical extension is unavailable at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#341 2020-07-21T13:55:01+0200
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => 'blanked',
'passwordsalt' => 'blanked',
'secret' => 'blanked',
'trusted_domains' =>
array (
0 => 'blanked',
1 => 'blanked',
),
'datadirectory' => '/home/data',
'dbtype' => 'mysql',
'version' => '19.0.1.1',
'overwrite.cli.url' => 'https://blanked',
'htaccess.RewriteBase' => '/',
'dbname' => 'blanked',
'dbhost' => 'localhost',
'dbport' => '',
'dbtableprefix' => 'oc_',
'mysql.utf8mb4' => true,
'dbuser' => 'blanked',
'dbpassword' => 'blanked',
'installed' => true,
'trusted_proxies' => 'blanked',
'ldapIgnoreNamingRules' => false,
'ldapProviderFactory' => 'OCA\\User_LDAP\\LDAPProviderFactory',
'maintenance' => false,
'theme' => '',
'loglevel' => 2,
'memcache.local' => '\\OC\\Memcache\\APCu',
'filelocking.enabled' => 'true',
'memcache.locking' => '\\OC\\Memcache\\Redis',
'redis' =>
array (
'host' => '/var/run/redis/redis-server.sock',
'port' => 0,
'timeout' => 1.5,
),
'mail_smtpmode' => 'smtp',
'mail_smtpsecure' => 'tls',
'mail_sendmailmode' => 'smtp',
'mail_from_address' => 'blanked',
'mail_domain' => 'blanked',
'mail_smtpauthtype' => 'LOGIN',
'mail_smtpauth' => 1,
'mail_smtphost' => 'blanked',
'mail_smtpport' => '587',
'mail_smtpname' => 'blanked',
'mail_smtppassword' => 'blanked',
'lost_password_link' => 'disabled',
'skeletondirectory' => '',
'simpleSignUpLink.shown' => false,
);
The output of your Apache/nginx/system log in /var/log/____:
[Tue Jul 21 00:00:03.967046 2020] [ssl:warn] [pid 1000] AH01909: blanked:443:0 server certificate does NOT include an ID which matches the server name
[Tue Jul 21 00:00:03.967365 2020] [ssl:warn] [pid 1000] AH01909: 127.0.1.1:443:0 server certificate does NOT include an ID which matches the server name
[Tue Jul 21 00:00:03.967492 2020] [mpm_prefork:notice] [pid 1000] AH00163: Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f configured -- resuming normal operations
[Tue Jul 21 00:00:03.967500 2020] [core:notice] [pid 1000] AH00094: Command line: '/usr/sbin/apache2'
[Tue Jul 21 08:43:27.941131 2020] [access_compat:error] [pid 20584] [client blanked:58788] AH01797: client denied by server configuration: /var/www/nextcloud/config
Please ignore the certificate warnings, there is a reverse proxy in front that handels ssl