KNOW HOW
Membership lists
PROTECT YOUR
WEB PAGES
f you re lucky enough to have been to a Formula and the information is sent back to the Web server.
Some Web pages
One Grand Prix, then you ll know that there is a The Web server then validates the username and
restrict access to
Imembers area and a VIP area. By entering these password against the information held in a password
areas you ll have immediate privileges and access not file. If the user passes the authentication (there is a
authorised members.
afforded to the general public. A similar thing can be username/password match) the page is displayed, if
If you ve ever
said about Web pages. Most Web pages you will not then the Web server throws up a 401 error page
want everyone to see, after all that s the whole point in the browser, see Figure 2.
wondered how this is
of the World Wide Web. On some pages, however,
done then wonder no
you may want to restrict the viewing to members or Setting up your password file
special users VIPs, if you will. To enable access to certain users, you first have to
more, David Tansley
You can protect Web pages based upon the calling create a password file. We will call our password file,
shows us how
browser, IP address, domain name or simply via .ht_users , though you can chose your own
password protection. We will look at the latter, which meaningful name if you wish.
is more commonly known as basic authentication. Now this is not the password
We will also look at how to personalise those nasty file that gets read when you
error messages that get thrown in your face when login to your Linux machine,
you try to go to a page that is missing (see Figure 1.) this is a totally different file.
or to an unauthorised area. To create this file we use the
htpasswd utility, which enables
The challenge/response process you to add users and their
First look at the process involved. Here s how it goes: passwords to an encrypted flat
you point your browser to a Web page protected by password file. As this file will
a username and password. The Web server then hold users names and
Figure 2: Authentication
looks for a file in that directory called .htaccess, if passwords it is best to stick this file (at least) off the
Failed. A 401 error page
that file is present it reads the directives main Web root directory. For goodness sake, DO NOT
(configuration) to obtain the type of authentication (if put it in your HTML, CGI-BIN or ICONS directory.
any) and what files to protect with this information; Create a new directory, called private say, off the
authentication begins. What happens now is www directory. (All Apache installs now stick your
commonly called the challenge/response cycle. The HTML (or HTDOCS), CGI-BIN and ICONS directory
Web server sends an authentication request to your within this www directory layout structure by
browser, the browser will prompt you for a user default.)
name and password within a dialog box. The user Next, lets create a couple of users, say davetan
enters their username/password then clicks on OK and paulinetan .:
$ mkdir private
$ pwd
/var/www/private
$ htpasswd -c /var/www/private/.ht_users
davetan
New password:
Re-type new password:
Adding password for user davetan
$ htpasswd /var/www/private/.ht_users
paulinetan
New password:
Re-type new password:
Figure 1: Requesting a non-existent
Adding password for user paulinetan
document. A 404 error page
17
Issue 18 " 2002 LINUX MAGAZINE
KNOW HOW
Notice that when adding user davetan Setting up the .htaccess file
we have used the -c after htpasswd. Now for the meaty part. Change into the directory
The -c option tells htpasswd that this where the HTML files you wish to protect are located
is a new file and thus a new file and create a .htaccess file. For example, to protect all
should be created. We give the full pages that start with the word private at the
pathname to the location of the beginning of the file, the following pattern match
passwd file(.ht_users). In this case we will do it for us:
are sticking the file in
private*.*
/var/www/private you may want to
use a different directory structure.
After a space, the username we are So the above pattern would match all of these files:
Figure 3: A
adding is given. Finally htpasswd prompts for private_main.html, privatepage1.html,
challenge/response
dialogue box.
password confirmations for that user. Adding user private_page2.html and private.php.
paulinetan, there is no need to specify the -c option Create a file called .htaccess with the following
as we do not want to create a new file, only append contents:
to it. If you use the -c, guess what, the file contents
AuthUserFile /var/www/private/.ht_users
previously held will be wiped.
AuthNAME Hey! Restricted Directory
Here s how the file we just created looks:
AuthTYPE Basic
$ more .ht_users
davetan:ETEkRxqtoentY
require valid-user
paulinetan:C.ePHk1ASFlIs
Notice the user names and password are colon
separated and the passwords are encrypted. In the first line, AuthUserFile instructs Apache where
the file we created to hold the usernames and
Informing the Apache Web server password is located. In the second line, AuthName is
By default, Apache comes pretty much secure. Locate the Realm Name you can use different realms to
the httpd.conf file and do a bit of editing. To find out protect different parts of your Web page directory
where your httpd.conf resides use the find utility to structure. For the basics, just use it as a header line
You can do all the work for you: that will be displayed on the dialog box when a
browser tries to access a protected page. You must
use
$ find / -name httpd.conf -print
enclose this with double quotes if you have more
/etc/httpd/conf/httpd.conf
different than one word, as above. In the third line, AuthTYPE
is basic; this means we are only using Basic
realms to
Next using vi, vim or some other text editor, edit Authentication, as mentioned at the beginning of the
protect http.conf and locate the directory directive: article.
different
AllowOveride entry within this directive, it will the files private*.* , which will protect all files that
parts of probably have: match this pattern. The require valid-user, means the
HTML page(s) matched will not be loaded unless the
your Web
AllowOverride None
user first gets successfully authenticated.
page Now load up the browser and point to a file that is
Change this to AllowOverride All , so you have an protected and you will get a challenge sent from the
directory
entry like so: server to your Web browser, similar to Figure 3. If you
hit cancel your browser will throw up a 401 error
page, as in Figure 2. Assuming you enter a correct
Options None
username/password, the protected page you
AllowOverride All
requested will be displayed.
Other examples
If you have made changes to your configuration file, To limit access to a page to a single user:
you must restart the Apache Web server. On a Red
Hat box with Apache put in place at installation,
require user davetan
you can use the rc script to stop/start the Apache
Web server:
$ /etc/rc.d/init.d/httpd restart
The above only allows the user davetan to access the
18
LINUX MAGAZINE Issue 18 " 2002
KNOW HOW
page top_secret.html
You may be thinking, what if somebody points
Listing 1: not_found404.html
their browser to an HTML directory and specifically
tries to load a .htaccess file. No problem, just deny I am sorry, but the file you requested could not be found,
it may
have been
viewing from everybody:
moved, deleted or simply just does not exist.
Back to Home
deny from all
If you have a query or something we should know about email the
administrator
at webadmin@localhost
The above file directive will set the state to deny from
everybody. Your .htaccess file is safe. If some one tries
to access it directly, a 403 forbidden error page will
be thrown up in their browser, saying it does not
have access to this file. Neat, eh?
Personalising error pages wrong. Listing 1,
Ever gone to a broken link and had a totally shows my very sparse,
unfriendly Not Found document thrown in your but more friendly
face? It is possible to make these pages friendlier to HTML code for a 404
the calling browser, however. There are quite a few error page.
error code pages on a Web server. The most common Please note that you
ones are: do not have to create
usernames/passwords
204 No content if you only wish to
401 Authorisation Required personalise your error
403 Forbidden pages, simply create a
404 Not Found .htaccess file and insert
500 Internal Server Error the entries for the
error pages you are
Figure 4:
Lets see how to create a 404 Not Found error personalising, as shown above.
Personalised 404
error page
page; the principles are the same for other error
pages you wish to personalise. All you need to do is Conclusion
put an entry in your .htaccess file (that you created I have demonstrated how to carry out basic
earlier). Like so: authentication on a Web server protecting individual
or many Web pages based via basic pattern
ErrorDocument 404 /icons/not_found404.html
matching. There are many more directives that you
can specify, however space does not allow me to go
Each ErrorDocument for a different error code must through all of them. When testing your .htaccess
go on a new line. The format of the entry is: configuration directives it is always a good idea to
open up a new shell window and continuously page
ErrorDocument
the end of your error log file, so you can pick up any
mis-configurations you may have in the .htaccess file
In the example shown above, I have put my error straight away and fix them. Like so:
document in /icons, which is off the Web root
$ tail -f error_log
directory. You are not restricted where you put these
HTML pages; some like to create a separate directory
and stick them in there it s up to you. Also notice When a user has been validated, they remain
the name I have given to the HTML page is a validated, even if they go off to another site then
meaningful one that corresponds to the actual error come back to view the same protected page again so
code page. In my example I have used long as they have not closed down their browser. To
not_fouund404.html, so I know it is concerned with re-set the authentication the calling browser must re-
the 404 error code page start their browser. Bear this in mind when testing
When throwing up personalised error pages it is your authentication procedures.
considered good practise to always put a link back to Being able to personalise your error pages, makes
Info
your homepage, or at least to some main Web site your Web site friendlier and more professional to a
Apache homepage:
(like http://www.netscape.com). There should also be user visiting your site. When these types of hiccups
www.apache.com
a way for the user to complain that some thing is do happen, it shows you care about your Web site.
19
Issue 18 " 2002 LINUX MAGAZINE
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