Security and Setup Warrnings

Nextcloud version (eg, 10.0.2): 12.0.3
Operating system and version (eg, Ubuntu 16.04): Ubuntu 16.04
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.18 (Ubuntu)
PHP version (eg, 5.6): 7.0.22-0ubuntu0.16.04.1
Is this the first time you’ve seen this error?: Yes

Can you reliably replicate it? (If so, please outline steps):
Set IIS to send the following HTTP response headers:
Strict-Transport-Security max-age=1576800; includeSubDomains
X-Content-Type-Options nosniff
X-Frame-Options SAMEORIGIN
X-XSS-Protection 1; mode=block

The issue you are facing:
In the Admin > Basic settings page, I’m getting the following errors:

  • The reverse proxy headers configuration is incorrect, or you are accessing Nextcloud from a trusted proxy. If you are not accessing Nextcloud from a trusted proxy, this is a security issue and can allow an attacker to spoof their IP address as visible to Nextcloud. Further information can be found in our documentation.
  • The "X-XSS-Protection" HTTP header is not configured to equal to "1; mode=block". This is a potential security or privacy risk and we recommend adjusting this setting.
  • The "X-Content-Type-Options" HTTP header is not configured to equal to "nosniff". This is a potential security or privacy risk and we recommend adjusting this setting.
  • The "X-Frame-Options" HTTP header is not configured to equal to "SAMEORIGIN". This is a potential security or privacy risk and we recommend adjusting this setting.

When I go to test, however, I show the following:

HTTP/1.1 200 OK =>
Keep-Alive => timeout=5, max=100
Content-Type => text/html; charset=UTF-8
Vary => Accept-Encoding
X-XSS-Protection => 1; mode=block
Strict-Transport-Security => max-age=15768000; includeSubDomains
X-Frame-Options => SAMEORIGIN
Content-Type-Options => nosniff
Date => Fri, 06 Oct 2017 21:27:32 GMT
Connection => close
Content-Length => 7273

The output of your Nextcloud log in Admin > Logging:

Warning	core	Login failed: '[redacted]' (Remote IP: '192.168.[ip].[address]')	October 06, 2017 15:36:57
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:56:02
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:56:02
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:56:01
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:58
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:57
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:57
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:53
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:52
Error	internet_connection_check	GuzzleHttp\Exception\RequestException: cURL error 56: Proxy CONNECT aborted	October 03, 2017 17:49:52
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 03, 2017 15:30:11
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:41:07
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:40:16
Warning	user_ldap	Configuration Error (prefix s02): login filter does not contain %uid place holder.	October 02, 2017 22:39:39
Warning	user_ldap	Configuration Error (prefix s02): Not a single Base DN given.	October 02, 2017 22:39:39
Warning	user_ldap	Configuration Error (prefix s02): No LDAP Login Filter given!	October 02, 2017 22:39:39
Warning	user_ldap	Configuration Error (prefix s02): No LDAP Port given!	October 02, 2017 22:39:38
Warning	user_ldap	Configuration Error (prefix s02): No LDAP Host given!	October 02, 2017 22:39:38
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:38:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:34
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:33
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:33
Error	PHP	ldap_search(): Partial search results returned: Sizelimit exceeded at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:25
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:25
Error	PHP	ldap_unbind(): supplied resource is not a valid ldap link resource at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:37:22
Error	PHP	ldap_bind(): Unable to bind to server: Can't contact LDAP server at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:37:22
Error	PHP	ldap_bind(): Unable to bind to server: Can't contact LDAP server at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:37:14
Error	PHP	ldap_bind(): Unable to bind to server: Can't contact LDAP server at /var/www/nextcloud/apps/user_ldap/lib/LDAP.php#293	October 02, 2017 22:37:14
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:37:10
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): either no password is given for theuser agent or a password is given, but not anLDAP agent.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): either no password is given for theuser agent or a password is given, but not anLDAP agent.	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:37:07
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:36:22
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:34:20
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:34:20
Warning	user_ldap	Configuration Error (prefix ): No LDAP Login Filter given!	October 02, 2017 22:34:20
Warning	user_ldap	Configuration Error (prefix ): No LDAP Port given!	October 02, 2017 22:34:20
Warning	user_ldap	Configuration Error (prefix ): login filter does not contain %uid place holder.	October 02, 2017 22:34:20
Warning	user_ldap	Configuration Error (prefix ): Not a single Base DN given.	October 02, 2017 22:34:20

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
Also shown here

<?php
$CONFIG = array (
'instanceid' => '[redacted]',
'passwordsalt' => '[redacted]',
'trusted_domains' =>
array (
0 => 'localhost',
1 => 'nextcloud',
2 => '192.168.[nextcloud].[ip]',
3 => 'cloud.[our].[domain]',
),
'datadirectory' => '/var/ncdata',
'version' => '12.0.3.3',
'dbtype' => 'mysql',
'dbhost' => 'localhost',
'dbport' => '',
'dbname' => '[redacted]',
'dbuser' => '[redacted]',
'dbpassword' => '[redacted]',
'dbtableprefix' => '[redacted]',
'installed' => true,
'default_language' => 'en',
'force_language' => 'en',
'knowledgebaseenabled' => true,
'allow_user_to_change_display_name' => false,
'auth.bruteforce.protection.enabled' => true,
'mail_domain' => '[our].[domain]',
'mail_from_address' => 'cloud',
'mail_smtpdebug' => true,
'mail_smtpmode' => 'smtp',
'mail_smtphost' => '192.168.[mailserver].[ip]',
'mail_smtpport' => '25',
'mail_smtptimeout' => 10,
'mail_smtpauth' => 1,
'mail_smtpauthtype' => 'LOGIN',
'mail_smtpname' => 'cloud',
'mail_smtppassword' => '[redacted]',
'overwritehost' => 'cloud.[our].[domain]',
'overwriteprotocol' => 'https',
'overwritewebroot' => '',
'overwritecondaddr' => '192\\.168\\.[mailserver]\\.[ip]$',
'overwrite.cli.url' => 'https://cloud.[our].[domain]/',
'htaccess.RewriteBase' => '/',
'trashbin_retention_obligation' => 'D10,D28',
'check_for_working_webdav' => true,
'check_for_working_wellknown_setup' => true,
'check_for_working_htaccess' => true,
'log_type' => 'file',
'logfile' => '/var/ncdata/nextcloud.log',
'loglevel' => '2',
'logdateformat' => 'F d, Y H:i:s',
'logtimezone' => 'America/Chicago',
'log_rotate_size' => '10485760',
'ldapUserCleanupInterval' => 41,
'ldapIgnoreNamingRules' => false,
'ldapProviderFactory' => '\\OCA\\User_LDAP\\LDAPProviderFactory',
'maintenance' => false,
'memcache.local' => '\\OC\\Memcache\\Redis',
'memcache.distributed' => '\\OC\\Memcache\\Redis',
'redis' =>
array (
'host' => '/var/run/redis/redis.sock',
'port' => 0,
'timeout' => 0,
'dbindex' => 0,
'password' => '[redacted]',
),
'mysql.utf8mb4' => true,
'secret' => '[redacted]',
'trusted_proxies' =>
array (
0 => '192.168.[mailserver].[ip]',
),
/**
 * Headers that should be trusted as client IP address in combination with
 * `trusted_proxies`. If the HTTP header looks like 'X-Forwarded-For', then use
 * 'HTTP_X_FORWARDED_FOR' here.
 *
 * If set incorrectly, a client can spoof their IP address as visible to
 * Nextcloud, bypassing access controls and making logs useless!
 *
 * Defaults to ``'HTTP_X_FORWARED_FOR'``
 */
'forwarded_for_headers' =>
array (
0 => 'HTTP_X_FORWARDED',
1 => 'HTTP_FORWARDED_FOR',
),
'filelocking.enabled' => true,
'filelocking.ttl' => 5400,
'memcache.locking' => '\\OC\\Memcache\\Redis',
'filelocking.debug' => false,
'debug' => false,
'mail_smtpsecure' => 'ssl',
);

The output of your Apache/nginx/system log in /var/log/____:

Oct  6 06:30:01 nextcloud CRON[14767]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 06:39:01 nextcloud CRON[14827]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 06:45:01 nextcloud CRON[14897]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 06:48:36 nextcloud systemd[1]: Starting Automatically fetch and run repair assertions...
Oct  6 06:48:36 nextcloud snap-repair[14927]: error: cannot use snap-repair on a classic system
Oct  6 06:48:36 nextcloud systemd[1]: Started Automatically fetch and run repair assertions.
Oct  6 06:54:25 nextcloud systemd[1]: Starting Daily apt upgrade and clean activities...
Oct  6 06:54:31 nextcloud systemd[1]: Started Daily apt upgrade and clean activities.
Oct  6 07:00:01 nextcloud CRON[15055]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 07:09:01 nextcloud CRON[15114]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 07:15:01 nextcloud CRON[15184]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 07:17:01 nextcloud CRON[15187]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 07:30:01 nextcloud CRON[15274]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 07:39:01 nextcloud CRON[15328]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 07:45:01 nextcloud CRON[15404]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 08:00:01 nextcloud CRON[15492]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 08:09:01 nextcloud CRON[15524]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 08:15:01 nextcloud CRON[15621]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 08:17:01 nextcloud CRON[15624]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 08:30:01 nextcloud CRON[15684]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 08:39:01 nextcloud CRON[15742]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 08:45:01 nextcloud CRON[15811]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 09:00:01 nextcloud CRON[15896]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 09:09:01 nextcloud CRON[15955]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 09:15:01 nextcloud CRON[16025]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 09:17:01 nextcloud CRON[16056]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 09:30:01 nextcloud CRON[16117]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 09:38:01 nextcloud CRON[16176]: (root) CMD (   test -x /etc/cron.daily/popularity-contest && /etc/cron.daily/popularity-contest --crond)
Oct  6 09:39:01 nextcloud CRON[16179]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 09:45:01 nextcloud CRON[16250]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 10:00:01 nextcloud CRON[16337]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 10:09:01 nextcloud CRON[16395]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 10:15:01 nextcloud CRON[16465]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 10:17:01 nextcloud CRON[16469]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 10:20:19 nextcloud snapd[909]: 2017/10/06 10:20:19.822332 snapmgr.go:429: No snaps to auto-refresh found
Oct  6 10:20:19 nextcloud snapd[909]: 2017/10/06 10:20:19.822332 snapmgr.go:429: No snaps to auto-refresh found
Oct  6 10:30:01 nextcloud CRON[16921]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 10:39:01 nextcloud CRON[16980]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 10:45:01 nextcloud CRON[17051]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 11:00:01 nextcloud CRON[17138]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 11:09:01 nextcloud CRON[17170]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 11:15:01 nextcloud CRON[17267]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 11:17:01 nextcloud CRON[17271]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 11:30:01 nextcloud CRON[17358]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 11:39:01 nextcloud CRON[17390]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 11:39:36 nextcloud systemd[1]: Starting Automatically fetch and run repair assertions...
Oct  6 11:39:37 nextcloud snap-repair[17431]: error: cannot use snap-repair on a classic system
Oct  6 11:39:37 nextcloud systemd[1]: Started Automatically fetch and run repair assertions.
Oct  6 11:45:01 nextcloud CRON[17468]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 12:00:01 nextcloud CRON[17556]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 12:09:01 nextcloud CRON[17614]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 12:15:01 nextcloud CRON[17684]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 12:17:01 nextcloud CRON[17715]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 12:30:01 nextcloud CRON[17775]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 12:39:01 nextcloud CRON[17834]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 12:45:01 nextcloud CRON[17905]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 13:00:01 nextcloud CRON[17994]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 13:09:01 nextcloud CRON[18052]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 13:15:01 nextcloud CRON[18122]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 13:17:01 nextcloud CRON[18126]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 13:30:01 nextcloud CRON[18213]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 13:39:01 nextcloud CRON[18272]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 13:45:01 nextcloud CRON[18343]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 13:50:19 nextcloud snapd[909]: 2017/10/06 13:50:19.921410 snapmgr.go:429: No snaps to auto-refresh found
Oct  6 14:00:01 nextcloud CRON[18430]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 14:09:01 nextcloud CRON[18488]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 14:15:01 nextcloud CRON[18558]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 14:17:01 nextcloud CRON[18561]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 14:30:01 nextcloud CRON[18650]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 14:39:01 nextcloud CRON[18682]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 14:45:01 nextcloud CRON[18780]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)Oct  6 14:45:01 nextcloud CRON[18780]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 15:00:01 nextcloud CRON[18840]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 15:09:01 nextcloud CRON[18899]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 15:15:01 nextcloud CRON[18969]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 15:17:01 nextcloud CRON[18999]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 15:30:01 nextcloud CRON[19058]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 15:30:33 nextcloud systemd[1]: Created slice User Slice of ncadmin.
Oct  6 15:30:33 nextcloud systemd[1]: Starting User Manager for UID 1000...
Oct  6 15:30:33 nextcloud systemd[1]: Started Session 164 of user ncadmin.
Oct  6 15:30:34 nextcloud systemd[19063]: Reached target Timers.
Oct  6 15:30:34 nextcloud systemd[19063]: Reached target Sockets.
Oct  6 15:30:34 nextcloud systemd[19063]: Reached target Paths.
Oct  6 15:30:34 nextcloud systemd[19063]: Reached target Basic System.
Oct  6 15:30:34 nextcloud systemd[19063]: Reached target Default.
Oct  6 15:30:34 nextcloud systemd[19063]: Startup finished in 144ms.
Oct  6 15:30:34 nextcloud systemd[1]: Started User Manager for UID 1000.
Oct  6 15:39:01 nextcloud CRON[19321]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 15:45:01 nextcloud CRON[19393]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 16:00:01 nextcloud CRON[19487]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 16:09:01 nextcloud CRON[19548]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 16:15:01 nextcloud CRON[19618]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 16:17:01 nextcloud CRON[19626]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Oct  6 16:21:15 nextcloud systemd[1]: Stopping LSB: Apache2 web server...
Oct  6 16:21:15 nextcloud apache2[19664]:  * Stopping Apache httpd web server apache2
Oct  6 16:21:16 nextcloud apache2[19664]:  *
Oct  6 16:21:16 nextcloud systemd[1]: Stopped LSB: Apache2 web server.
Oct  6 16:21:16 nextcloud systemd[1]: Starting LSB: Apache2 web server...
Oct  6 16:21:16 nextcloud apache2[19689]:  * Starting Apache httpd web server apache2
Oct  6 16:21:16 nextcloud apache2[19689]: AH00558: apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1. Set the 'ServerName' directive globally to suppress this message
Oct  6 16:21:17 nextcloud apache2[19689]:  *
Oct  6 16:21:17 nextcloud systemd[1]: Started LSB: Apache2 web server.
Oct  6 16:30:01 nextcloud CRON[19790]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 16:39:01 nextcloud CRON[20215]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 16:45:01 nextcloud CRON[20285]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 17:00:01 nextcloud CRON[20384]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 17:01:36 nextcloud systemd[1]: Starting Cleanup of Temporary Directories...
Oct  6 17:01:36 nextcloud systemd-tmpfiles[20386]: [/usr/lib/tmpfiles.d/var.conf:14] Duplicate line for path "/var/log", ignoring.
Oct  6 17:01:36 nextcloud systemd[1]: Started Cleanup of Temporary Directories.
Oct  6 17:09:01 nextcloud CRON[20448]: (root) CMD (  [ -x /usr/lib/php/sessionclean ] && /usr/lib/php/sessionclean)
Oct  6 17:15:01 nextcloud CRON[20527]: (www-data) CMD (php -f /var/www/nextcloud/cron.php > /dev/null 2>&1)
Oct  6 17:17:01 nextcloud CRON[20530]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)

Error message log:

[Fri Oct 06 06:25:11.575271 2017] [ssl:warn] [pid 7479] AH01909: cloud.[our].[domain]:443:0 server certificate does NOT include an ID which matches the server name
[Fri Oct 06 06:25:11.576397 2017] [mpm_prefork:notice] [pid 7479] AH00163: Apache/2.4.18 (Ubuntu) OpenSSL/1.0.2g configured -- resuming normal operations
[Fri Oct 06 06:25:11.576409 2017] [core:notice] [pid 7479] AH00094: Command line: '/usr/sbin/apache2'
[Fri Oct 06 16:21:15.973389 2017] [mpm_prefork:notice] [pid 7479] AH00169: caught SIGTERM, shutting down
[Fri Oct 06 16:21:16.927944 2017] [ssl:warn] [pid 19707] AH01909: cloud.[our].[domain]:443:0 server certificate does NOT include an ID which matches the server name
[Fri Oct 06 16:21:17.037209 2017] [ssl:warn] [pid 19708] AH01909: cloud.[our].[domain]:443:0 server certificate does NOT include an ID which matches the server name
[Fri Oct 06 16:21:17.043536 2017] [mpm_prefork:notice] [pid 19708] AH00163: Apache/2.4.18 (Ubuntu) OpenSSL/1.0.2g configured -- resuming normal operations
[Fri Oct 06 16:21:17.043575 2017] [core:notice] [pid 19708] AH00094: Command line: '/usr/sbin/apache2'

Finally got the reverse proxy working most of the way except for the home page image. I was able to disable SSL offloading from IIS, as well as remove the IIS response headers, and the warnings disappeared.