linux-server-setup/exercises/h4.md

Linux servers - Exercice 4

Disclaimer:

This exercise is a part of Linux servers (ICT4TN021, spring 2018) // Linux-palvelimet (ICT4TN021, kevät 2018) school course organized as a part of Information Technology studies in Haaga-Helia university of Applied Sciences, Helsinki, Finland. Course lecturer Tero Karvinen has defined the original assignment descriptions in Finnish presented in this document in English. Answers and translations have been written by Pekka Helenius (me, ~ Fincer).

a) Make it possible to create home pages with normal user privileges in your virtual server environment.

Answer:

Virtual server IP address is 174.138.2.190. The server is hosted on DigitalOcean which provides hosting services for users. Ubuntu 16.04 LTS (without DE) is used as a server platform.

Ubuntu distribution hosted on DigitalOcean has custom configurations compared to Canonical version of clean Ubuntu environment. For example, DigitalOcean has predefined different repository sources in package manager sources file /etc/apt/sources.list (http://mirrors.digitalocean.com/ubuntu/) and has customized configuration for Apache web server by default. Can you trust these repositories and predefined configurations as a system administrator? Can you be sure the program source codes are "clean" and do not contain malicious code patches? Are the used package repositories updated and which flags have been used to compile the binary software available there? What differences are there between the official Canonical and DigitalOcean repositories?

It is good to stop to think the previous issues before looking for a third party hosting service for your server environment. Do available markets have better virtual hosting service providers and in which criteria? In small business, it can be safer to hold all the aces and set up a minimal self-hosted server using a computer (suited for your needs) such as Raspberry Pi and claim a Domain name for it from a DNS provider. If you do larger business, you need to consider your server capacity again. It can be more profitable and comfortable to buy some server space from a virtual hosting server provider.

Of course, if you ever want to, you can install the server environment from scratch using rolling releases such as Arch Linux, Gentoo or 'Linux from Scratch'. However, this is not recommended approach in server environments requiring system stability over newer software.

Anyway,

1. Do initial configuration for your server following the guide by Tero Karvinen:

Tero Karvinen - First Steps on a New Virtual Private Server – an Example on DigitalOcean and Ubuntu 16.04 LTS

2. Connect to your new virtual private server once you have set it up. I use a predefined user name newuser in my server environment:

phelenius@my-machine:~$ ssh newuser@174.138.2.190
newuser@174.138.2.190's password: 
Welcome to Ubuntu 16.04.3 LTS (GNU/Linux x86_64)
* Documentation:  https://help.ubuntu.com
* Management:     https://landscape.canonical.com
* Support:        https://ubuntu.com/advantage
Get cloud support with Ubuntu Advantage Cloud Guest:
http://www.ubuntu.com/business/services/cloud
7 packages can be updated.
0 updates are security updates.
Last login: Tue Feb 13 14:49:24 2018 from XXX.XXX.XXX.XXX
newuser@goauldhost:~$ 

3. Open default SSH TCP port 22 in your firewall:

NOTE! Default policy for Ubuntu firewall is to deny/drop all input connections so we need to allow traffic into protocol/daemon specific ports to open up communication between this server and clients.

newuser@goauldhost:~$ sudo ufw allow 22/tcp && sudo ufw enable

Once you have established SSH connection to your remote server, install apache2 and open port 80 for it doing the following:

newuser@goauldhost:~$ sudo apt-get install apache2 && sudo ufw allow 80/tcp

4. Enable Apache userdir module:

newuser@goauldhost:~$ sudo a2enmod userdir

5. Some PHP and userdir module related configurations seem to be predefined in packages provided on DigitalOcean server environment (such as # symbols in /etc/apache2/mods-enabled/php7.0.conf in order to enable PHP for user sites), unlike stated in Exercise 3.

6. Restart Apache HTTP daemon (HTTPD) after enabling userdir module:

newuser@goauldhost:~$ sudo systemctl restart apache2.service

Recheck HTTP daemon state (should be Running):

newuser@goauldhost:~$ systemctl status apache2.service

If everything seem to be running and working you can try to establish connection to the HTTP daemon server using your local computer (do not try this in your virtual private server environment but with an external client computer):

phelenius@my-machine:~$ xdg-open http://174.138.2.190:80

The IP address here refers to the virtual private server IP address.

7. If the connection test is successful, you should see something similar to this picture:

Let's get back to the virtual server environment in our SSH session.

8. We should hide any extra server information which is visible for clients. Add the following lines in /etc/apache2/apache2.conf (with sudoedit):

TraceEnable Off
ServerSignature Off
ServerTokens Prod

Description of these lines here.

Restart Apache HTTP daemon (web server):

newuser@goauldhost:~$ sudo systemctl restart apache2.service

9. Create a new user monkey (finnish: apina). We do not add this user to sudo groups, therefore denying all root access for this user:

newuser@goauldhost:~$ sudo adduser monkey

Change to the default shell of user monkey (you can check it by executing: grep monkey /etc/passwd):

newuser@goauldhost:~$ su monkey
Password: 
monkey@goauldhost:/home/newuser$ cd
monkey@goauldhost:~$ mkdir public_html

Therefore we have created a new home site folder for the user monkey. Contents of this folder should be available like shown in the following picture:

NOTE! As you can see, Apache doesn't give any server information in the website view, thanks for the configurations done in step 8.

User monkey can add any content to his/her personal site. By default, Apache looks for any of the following files, defined in /etc/apache2/mods-available/dir.conf (symbolic link in folder /etc/apache2/mods-enabled/dir.conf):

newuser@goauldhost:~$ ls -l /etc/apache2/mods-enabled/dir.conf
lrwxrwxrwx 1 root root 26 Feb  8 10:40 /etc/apache2/mods-enabled/dir.conf -> ../mods-available/dir.conf
newuser@goauldhost:~$ cat /etc/apache2/mods-enabled/dir.conf |grep -i directoryindex | awk '{$1 = ""; print $i}'
index.html index.cgi index.pl index.php index.xhtml index.htm

Permissions of folder $HOME/public_html of the user monkey are as follows:

monkey@goauldhost:~$ ls -l
total 4
drwxrwxr-x 2 monkey monkey 4096 Feb 13 15:35 public_html

drwxrwxr-x 123456789 10

d = directory r = read (value 4) w = write (value 2) x = execute (value 1)

where ...symbols 2-4 (rwx) indicate permissions of the user monkey to the folder ...symbols 5-7 (rwx) indicate permissions of the (primary) group where the user monkey belongs to. In this case, the group is monkey ...symbols 8-10 (r-x) indicate permissions granted for other system users to the folder

Permissions can be written in numeric form but also in symbolic form. For example,

775 = rwxrwxr-x (4+2+1, 4+2+1, 4+1) ug=rwx,o=rx = rwxrwxr-x

Take a look on the following links to get more information about Unix permissions:

• Arch Wiki - File permissions and attributes

• Wikipedia - Notation_of_traditional_Unix_permissions

• Arch Wiki - umask

Changing permissions is recommended to be done in symbolic mode because individual permissions can't be as flexibly be changed in numeric mode.

ls command shows a user (monkey) first after which group (monkey) is shown.

The folder is accessible in public network via address http://174.138.2.190:80/~monkey/

You can change permissions with chmod command.

Numeric form: chmod 775 ~/public_html

Symbolic form: chmod ug=rwx,o=rx ~/public_html

You can change permissions recursively using -R parameter (chmod -R ...)

EXTRA: Deleting Server field from HTTP header by updating Apache source code on Debian-based Linux distributions

Including Server field in HTTP header by Apache HTTP daemon (web server) is debated. HTTP/1.1 standard specification states the following:

Note: Revealing the specific software version of the server might allow the server machine to become more vulnerable to attacks against software that is known to contain security holes. Server implementors are encouraged to make this field a configurable option.

NOTE! Apache is compiled from source code.

Removal of Server field from HTTP header is debated in Apache developers' community (The key question here: does removal of the field actually improve any security?). More about this topic: StackoverFlow (Can't remove Server: Apache header).

NOTE! The following method does not work with automatic system updates via package repositories (usage of sudo apt-get update and sudo apt-get upgrade commands) because the patches binary files would be replaced by ones available in the official repositories. Therefore, each time you want to update your Apache server, you need to recompile it from source applying the patch file provided in this GitHub repository. This method can be troublesome for system administration or contain unaccepted policy in your company. Consider using puppet or salt or any relevant automation method here.

NOTE! You must be aware what you are doing each time you compile software from source. Trust the source, trust the patch files (diff or patch) and do not do anything that can lead to unknown or troublesome bugs, malicious code execution or create new security risks.

NOTE! We are unable to sign the package with the official maintainer key because we update Apache with our specific patch file and compile the software ourselves. Therefore we ignore any signing requirements in dpkg-buildpackage command (or alternatively we can use our own keys).

NOTE Consider any policy that determines your production and/or server environment requirements. For example: Am I allowed to install software from source code? Does my method break a (critical) component in working server environment? Etc.

NOTE! Again. Know exactly what you are about to do. As a system administrator you hold responsibility here.

We have already improved security of our Apache web server by removing critical information sent to client. However, the server still gives information about its name as follows:

newuser@goauldhost:~/source_codes/apache2$ curl -I http://localhost
HTTP/1.1 200 OK
Date: Sat, 17 Feb 2018 13:27:11 GMT
Server: Apache
Content-Type: text/html;charset=UTF-8

We want to remove field Server: Apache. Multiple approaches were tested (such as modsecurity2 module and writing line Header unset Server into file /etc/apache2/apache2.conf) without success. Therefore I ended up patching the source code of Apache web server so that the wanted field can really be removed.

Download Apache source code on your Debian-based Linux distribution:

newuser@goauldhost:~$ mkdir -p ./source_codes/apache2 && cd ./source_codes/apache2
newuser@goauldhost:~/source_codes/apache2$ apt-get source apache2

After which add source code patch file into created $HOME/source_codes/apache2 folder.

NOTE! I have personally created the patch file with Unix tool diff. The patch file is not downloaded from any suspicious website. You can always check the patch file code yourself if still hesitating.

If you have a working Apache HTTP daemon (web server) environment on your Linux, please check the version of your Apache software version with the following command:

newuser@goauldhost:~$ dpkg -s apache2 |grep -i version
Version: 2.4.18-2ubuntu3.5

In that way we can be sure version of the downloaded source code matches with our already-installed Apache environment.

Once you have downloaded the source code, go to the following folder (which contains the code):

newuser@goauldhost:~/source_codes/apache2$ cd apache2-2.4.18/

Implement the patch file changes into the Apache source code:

newuser@goauldhost:~/source_codes/apache2/apache2-2.4.18$ patch -Np1 -i ../patch_apache_servertokens.patch

Before compiling Apache web server, you must install the following build time dependencies:

newuser@goauldhost:~/source_codes/apache2/apache2-2.4.18$ sudo apt-get install debhelper libaprutil1-dev libapr1-dev libpcre3-dev zlib1g-dev libssl-dev liblua5.1-0-dev libxml2-dev autotools-dev build-essential

Compile and install the Apache web server:

newuser@goauldhost:~/source_codes/apache2/apache2-2.4.18$ dpkg-buildpackage -rfakeroot -b -us -uc ... ...

```

If Apache HTTP daemon is running, stop it:

newuser@goauldhost:~/source_codes/apache2$ sudo systemctl stop apache2.service

It is essential to check which apache2 packages have been installed into the target system. We want to install only specific deb packages already found in the system, as multiple deb packages have been compiled by the previous command. All found Apache2 packages in the system should be replaced by the ones compiled from the Apache2 source code.

System has the following Apache2 packages:

newuser@goauldhost:~/source_codes/apache2/apache2-2.4.18$ cd ..
newuser@goauldhost:~/source_codes/apache2$ dpkg --get-selections |grep apache | awk '{print $1}'
apache2
apache2-bin
apache2-data
apache2-utils
libapache2-mod-php
libapache2-mod-php7.0

Then we compare the above list to the compiled deb packages:

newuser@goauldhost:~/source_codes/apache2$ ls |grep deb
apache2_2.4.18-2ubuntu3.5_amd64.deb
apache2_2.4.18-2ubuntu3.5.debian.tar.xz
apache2-bin_2.4.18-2ubuntu3.5_amd64.deb
apache2-data_2.4.18-2ubuntu3.5_all.deb
apache2-dbg_2.4.18-2ubuntu3.5_amd64.deb
apache2-dev_2.4.18-2ubuntu3.5_amd64.deb
apache2-doc_2.4.18-2ubuntu3.5_all.deb
apache2-suexec-custom_2.4.18-2ubuntu3.5_amd64.deb
apache2-suexec-pristine_2.4.18-2ubuntu3.5_amd64.deb
apache2-utils_2.4.18-2ubuntu3.5_amd64.deb

... as a result we can see that the following deb packages should be installed with dpkg -i command:

newuser@goauldhost:~/source_codes/apache2$ sudo dpkg -i apache2_2.4.18-2ubuntu3.5_amd64.deb apache2-bin_2.4.18-2ubuntu3.5_amd64.deb apache2-data_2.4.18-2ubuntu3.5_all.deb apache2-utils_2.4.18-2ubuntu3.5_amd64.deb

If everything has succeeded you should have a working, patched Apache web server in your target system. Because the patches web server software supports ServerTokens None option now, we shall add this option into etc/apache2/apache2.conf.

newuser@goauldhost:~$ sudoedit /etc/apache2/apache2.conf

Add the following lines (// just replace ServerTokens Prod with None):

TraceEnable Off
ServerSignature Off
ServerTokens None

NOTE! Any settings in /etc/apache2/conf-available/security.conf overrides these configuration changes.

Restart Apache2 server (you must apply the patch file before doing this because the default Apache software does not implement 'None' for ServerTokens):

newuser@goauldhost:~$ sudo systemctl start apache2.service

Check whether the configuration works:

phelenius@my-machine:~$ curl -I http://174.138.2.190
HTTP/1.1 200 OK
Date: Sat, 17 Feb 2018 14:02:20 GMT
Last-Modified: Wed, 14 Feb 2018 00:06:44 GMT
ETag: "20b-56520e2f88f4a"
Accept-Ranges: bytes
Content-Length: 523
Vary: Accept-Encoding
Content-Type: text/html

Therefore we have successfully deleted Server field from HTTP header.

You can additionally set and unset HTTP header fields sent to a client as follows:

Header unset Last-Modified
Header unset Accept-Ranges
Header unset Vary
Header unset ETag

You must be careful when unsetting fields because it affects behavior of client programs and efficiency of your server environment (performance, for example). Remember that factors such as field order, formatting and error messages can give hints about the used server environment as well (for example, 404 not found message).

NOTE! The header options mentioned above work only if module 'headers' has been activated (run command sudo a2enmod headers and restart the server)

More about HTTP header in Wikipedia. More articles in ETag, Vary: Accept-Encoding, etc.

s) Set user default website to be the default website for Apache in your virtual server environment.

Answer:

Let's begin from the final state of the previous answer. We have created a user monkey in our server computer. This user has a website URL 174.138.2.190:80/~monkey

1. Remove default webpage of Apache web server, and move DocumentRoot to point to directory $HOME/public_html of user monkey, after which restart Apache service daemon.

newuser@goauldhost:~$ sudo sed -i 's?DocumentRoot /var/www/html?DocumentRoot /home/monkey/public_html?' /etc/apache2/sites-available/000-default.conf

We can disable folder path /var/www commenting out the following lines (inserting # symbols) in file /etc/apache2/apache2.conf (use command sudoedit, for example):

#<Directory /var/www/>
#        Options Indexes FollowSymLinks
#        AllowOverride None
#        Require all granted
#</Directory>

Restart Apache web server daemon:

newuser@goauldhost:~$ sudo systemctl restart apache2.service

Go to the following IP address with your local computer (use HTTP port 80):

xdg-open http://174.138.2.190:80

The opening view should be as follows:

2. Create a new file index.html in the directory $HOME/public_html of user monkey (where $HOME=/home/monkey/)

newuser@goauldhost:~$ su monkey
Password: 
monkey@goauldhost:/home/newuser$ cd
monkey@goauldhost:~$ echo -e '<!DOCTYPE html>\n <html>\n \t<head>\n \t\t<title>Testi</title>\n \t</head>\n \t<body>\n \t\t<h1>Testi</h1>\n \t</body>\n </html>\n' > ~/public_html/index.html

3. We should redirect all index.html traffic to the folder root _/home/monkey/public_html/. This can be done by creating hidden page-related control file .htaccess file to the directory root.

monkey@goauldhost:~$ cd public_html
monkey@goauldhost:~/public_html$ touch .htaccess
monkey@goauldhost:~/public_html$ echo -e '<IfModule mod_rewrite.c>\n\tRewriteEngine On\n\tRewriteBase /\n\tRewriteRule ^index\.html$ / [NC,R,L]\n</IfModule>' | tee -a ./.htaccess

Reactivate Apache module 'rewrite'. We shall switch our user because user monkey doesn't have sudo rights at this point:

monkey@goauldhost:~/public_html$ su newuser
Password: 
newuser@goauldhost:/home/monkey/public_html$ sudo a2enmod rewrite
Enabling module rewrite.
To activate the new configuration, you need to run:
service apache2 restart
newuser@goauldhost:/home/monkey/public_html$ sudo systemctl restart apache2.service

Your Apache web server should redirect all traffic of http://174.138.2.190:80/index.html to address http://174.138.2.190:80/

y) Find clues of possible penetration attempts to your web server. You can find more information about suspicious IP address without connecting them by using commands ipcalc, geoiplookup and whois, for instance.

Answer:

At the time of writing this answer, the Apache web server was running bit over a week period. However, there were no any webpage deployed during that time, and therefore my web server hadn't created any major log entries. However, I noticed one suspicious connection attempt to setup.php file of phpMyAdmin software, although the software was not installed. The lookup was done by checking web server log file var/log/apache2/access.log. The log entry itself was as follows:

66.118.142.165 - - [13/Feb/2018:14:43:58 +0000] "HEAD /phpmyadmin/scripts/setup.php HTTP/1.0" 404 159 "-" "-"

We shall analyze the logged IP address (+ download a georeferred IP database to determine more specific geolocation of the source by using wget command):

newuser@goauldhost:~$ sudo apt-get -y install geoip-bin
newuser@goauldhost:~$ wget http://geolite.maxmind.com/download/geoip/database/GeoLiteCity.dat.gz
newuser@goauldhost:~$ gunzip GeoLiteCity.dat.gz
newuser@goauldhost:~$ OBSIP=66.118.142.165
newuser@goauldhost:~$ echo -e "Server Geolocation:\n$(geoiplookup -f /home/newuser/GeoLiteCity.dat $OBSIP)\n\n$(nslookup $OBSIP)\n\nDNS Name:\n$(dig +short -x $OBSIP)" && unset OBSIP

Output is as follows:

Server Geolocation:
GeoIP City Edition, Rev 1: US, FL, Florida, Tampa, 33611, 27.886700, -82.511703, 539, 813
Server:		67.207.67.2
Address:	67.207.67.2#53
Non-authoritative answer:
165.142.118.66.in-addr.arpa	name = 66-118-142-165.static.sagonet.net.
Authoritative answers can be found from:
DNS Name:
66-118-142-165.static.sagonet.net.

The log entry tells us that connection to page http://174.138.2.190:80/phpmyadmin/scripts/setup.php was tried to establish. The server responded with code 404 (HTTP_NOT_FOUND), indicating that the address couldn't be found. It is seen that user agent string of 66.118.142.165 is empty (just a line). It is known that the user agent string can be very easily customized.

HTTP HEAD method were used in the connection attempt. The HTTP HEAD method is more suitable for quick file existence look-ups than HTTP GET method because only the file existence is checked, leading to decreased data transfer rates between a server and a client. The HEAD method is usually used for caching documents (data). A client program just tries to download metadata of the request document from a server. Apache web server does not return the message response body while answering to the client program with the HTTP HEAD method..

the HEAD method can be "disabled" by adding the following lines into 1) file ~/public_html/.htaccess (in the case of this assignment) 2) or into file /etc/apache2/sites-available/000-default.conf 3) or any site-specific configuration file in Apache's sites-available folder 4) or any .htaccess file in a website directory root:

RewriteEngine on
RewriteCond %{THE_REQUEST} !^(POST|GET)\ /.*\ HTTP/1\.1$ 
RewriteRule .* - [F,L]

The original answer here

It is understandable that line RewriteEngine on doesn't need to be determined twice and adding this code requires re-enabling of Apache rewrite module.

I have had a Debian-based web server (LAMP) environment in the past years. I have included Apache access.log parts of that web server environment here (year 2014):

Apache - access.log, example

The log file reveals many suspicious connection attempts from Thailand and Netherlands, for example.

The most memorable log entry from the past years was, however, a penetration attempt by Romanian hacker/bot group and it looked like the following:

4.125.148.79 - - [07/Aug/2013:20:53:35 +0400] "GET /w00tw00t.at.blackhats.romanian.anti-sec:) HTTP/1.1" 404 142 "-" "ZmEu"

y) Create a set of websites on your local computer and copy the sites to your web server with scp command.

Answer:

1. Let's create the required websites locally, after which the upload is done with user newuser. I have used pre-created websites in this assignment. The upload is done with my Arch Linux computer using required SSH protocol:

[13/02/2018 21:04:16 - fincer: ~ ]$ scp /home/fincer/Documents/website/website_1.03_fincer.zip newuser@174.138.2.190:./
The authenticity of host '174.138.2.190 (174.138.2.190)' can't be established.
ECDSA key fingerprint is SHA256:XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '174.138.2.190' (ECDSA) to the list of known hosts.
newuser@174.138.2.190's password: 
website_1.03_fincer.zip                                                                    100%  656KB 655.8KB/s   00:01    
[13/02/2018 21:04:32 - fincer: ~ ]$ 

2. Modify Apache default webpage address to point to /home/newuser/public_html/:

newuser@goauldhost:~$ sudo sed -i 's?DocumentRoot /home/monkey/public_html?DocumentRoot /home/newuser/public_html?' /etc/apache2/sites-available/000-default.conf
newuser@goauldhost:~$ sudo systemctl restart apache2.service

3. Because /home/newuser/public_html/ is empty (checked with ls command), we shall extract uploaded website_1.03_fincer.zip to that directory.

newuser@goauldhost:~$ sudo apt-get update && sudo apt-get install unzip
newuser@goauldhost:~$ mv website_1.03_fincer.zip ./public_html/ && cd ./public_html
newuser@goauldhost:~$ unzip website_1.03_fincer.zip

4. It should be possible to open the website using URL 174.138.2.190, and the website should look like the following:

5. Let's copy another website sample into folder $HOME/public_html/ of user monkey:

[13/02/2018 22:01:40 - fincer: ~ ]$ scp /home/fincer/Documents/server_site.tar.xz monkey@174.138.2.190:./public_html/

6. Let's establish a new SSH connection to the virtual server computer with user monkey:

[13/02/2018 22:04:23 - fincer: ~ ]$ ssh monkey@174.138.2.190

7. In the virtual web server computer terminal, go to _$HOME/public_html/ of user monkey, extract server_site.tar.xz and put the extracted files into correct places in the directory hierarchy. Rename old index.html file to index.html.old

monkey@goauldhost:~/public_html$ mv index.html index.html.old
monkey@goauldhost:~/public_html$ tar xf server_site.tar.xz
monkey@goauldhost:~/public_html$ mv ./server_site/* ./
monkey@goauldhost:~/public_html$ rm -Rf ./{server_site,server_site.tar.xz}

(you could have just used one * symbol in the previous rm command because the equal name syntax)

The deployed website can be viewed in URL address http://174.138.2.190:80/~apina, and they look as follows (this example is a work time // wage calculator):

y) Set up a simple PHP webpage on your web server. For instance, you can print a remote address of the user ( $_SERVER['REMOTE_ADDR'] ) etc. Be careful if you use input forms of any kind.

Answer:

In this answer, I add a PHP-based BMI calculator (Body Mass Index) to my website. For this purpose, two files were created: bmicalc.html and bmicalc.php which both are uploaded to the virtual web server with the following command, executed at the local computer:

phelenius@my-machine:~$ scp $HOME/public_html/bmi-index/{bmicalc.php,bmicalc.html} newuser@174.138.2.190:./public_html/
newuser@174.138.2.190's password:
bmicalc.php                                                           100% 3051     3.0KB/s   00:00    
bmicalc.html                                                          100%  523     0.5KB/s   00:00 

The following image demonstrates a web browser view of URL address 174.138.2.190/bmicalc.html. On the left side: the source code of the HTML page. On the right side: server-side "raw" PHP source code which is not seen by the client program, our web browser in this case (PHP code = server-side execution/only web server sees the code, JavaScript code = client-side execution/client can see the code, too):

Edit The following changes has been done after answering the assignment:

• PHP-related HTTP method GET has been changed to POST method afterwards because usage of the GET method leads to visible input values in a web browser URL field. This doesn't happen when using the POST method.

• Implementation of server-side solutions which restrict user accessibility to other web server directories and files.

• PHP code has been merged with the HTML document, i.e. there is no additional .php file in the web server anymore.