This tutorial surveys the current methods for restricting access to documents stored on the Why? InterNetworking web server. The tutorial also walks through setup and use of these methods.
Why? InterNetworking allows access restriction based on several criteria:
This tutorial is based largely on the work done by the NCSA httpd development team.
In Basic HTTP Authentication, the password is passed over the network not encrypted but not as plain text -- it is "uuencoded." Anyone watching packet traffic on the network will not see the password in the clear, but the password will be easily decoded by anyone who happens to catch the right network packet.
So basically this method of authentication is roughly as safe
as telnet
or ftp style username and
password security.
In MD5 Message Digest Authentication, the password is not
passed over the network at all. Instead, a series of numbers is
generated based on the password and other information about the
request, and these numbers are then hashed using MD5. The
resulting "digest" is then sent over the network, and
it is combined with other items on the server to test against the
saved digest on the server. This method is more secure over the
network, but it has a penalty. The comparison digest on the
server must be stored in a fashion that it is retrievable. Basic
Authentication stores the password using the one way crypt()
function. When the password comes across, the server uudecodes it
and then crypts it to check against the stored value. There is no
way to get the password from the crypted value. In MD5, you need
the information that is stored, so you can't use a one way
hashing function to store it. This means that MD5 requires more
rigorous security on the server machine. It is possible, but
non-trivial, to implement this type of security under the UnixTM
security model.
MD5 Message Digest Authentication is not covered in this document.
You should use the htpasswd
program to create the
ID and Password files used by the web server. This is available
by telneting to the server and running "htpasswd." If
you do not have unix shell access to the web server (individual
and corporate lite accounts) or do not want to log into the web
server, "unsupported" DOS
and Windows versions of htpasswd are
available (They work to the best of our knowledge, but we are
only able to provide support for the Unix shell version.) The
htpasswd program's use is documented below.
This should help you set up protection on a directory via the Basic HTTP Authentication method. This method also uses the standard plaintext password file. If you have a large user base, NCSA HTTPd supports a DBM based password file for faster access.
So let's suppose you want to restrict files in a directory
called turkey
to username pumpkin
and
password pie
. Here's what to do:
Create a
file called .htaccess
in directory turkey
that looks like this:
AuthUserFile /home/corp/johndoe/.htpasswd AuthGroupFile /dev/null AuthName ByPassword AuthType Basic <Limit GET> require user pumpkin </Limit>
Note that the password file will be in another directory (/home/corp/johndoe).
AuthUserFile must be the full Unix pathname of the password file.
Also note that in this case there is no group file, so we
specify /dev/null
(the standard Unix way to say
"this file doesn't exist").
AuthName
can be anything you want. The AuthName
field gives the Realm name for which the protection is provided.
This name is usually given when a browser prompts for a password,
and is also usually used by a browser in correlation with the URL
to save the password information you enter so that it can
authenticate automatically on the next challenge. Note: You
should set this to something, otherwise it will default to
"ByPassword," which is both non-descriptive and too
common.
AuthType
should be set to Basic
,
since we are using Basic HTTP Authentication. Other possibilities
are PEM, PGP, KerberosV4, KerberosV5, or Digest. These other
types of authentication will be discussed later.
In this example, only the method GET is restricted using the LIMIT
directive. To limit other methods (particularly in CGI
directories), you can specify them separated by spaces in the LIMIT
directive. For example:
<LIMIT GET POST PUT> require user pumpkin </LIMIT>
If you only use GET
protection for a CGI script,
you may be finding that the REMOTE_USER
environment
variable is not getting set when using METHOD="POST"
,
obviously because the directory isn't protected against POST
.
Create
the password file /home/corp/johndoe/.htpasswd
The easiest way to do this is to use the htpasswd
program distributed with NCSA HTTPd. Do this:
htpasswd -c /home/corp/johndoe/.htpasswd pumpkin
Type the password -- pie
-- twice as instructed.
Check the resulting file to get a warm feeling of self-satisfaction; it should look like this:
pumpkin:y1ia3tjWkhCK2
That's all. Now try to access a file in directory turkey
-- your browser should demand a username and password, and not
give you access to the file if you don't enter pumpkin
and pie
. If you are using a browser that doesn't
handle authentication, you will not be able to access the
document at all.
If you want to give access to a directory to more than one username/password pair, follow the same steps as for a single username/password with the following additions:
Add
additional users to the directory's .htpasswd
file.
Use the htpasswd
command without the -c
flag to add additional users; e.g.:
htpasswd /home/corp/johndoe/.htpasswd peanuts htpasswd /home/corp/johndoe/.htpasswd almonds htpasswd /home/corp/johndoe/.htpasswd walnuts
Create a group file.
Call it /home/corp/johndoe/.htgroup
and have it look something like this:
my-users: pumpkin peanuts almonds walnuts
...
where pumpkin
, peanuts
,
almonds
, and walnuts
are the usernames.
Then
modify the .htaccess
file in the
directory to look like this:
AuthUserFile /home/corp/johndoe/.htpasswd AuthGroupFile /home/corp/johndoe/.htgroup AuthName ByPassword AuthType Basic <Limit GET> require group my-users </Limit>
Note that AuthGroupFile
now points to your group
file and that group my-users
(rather than individual
user pumpkin
) is now required for access.
That's it. Now any user in group my-users
can use
his/her individual username and password to gain access to
directory turkey
.
Following are several examples of the range of access authorization capabilities available through the Why? InterNetworking web server. The examples are served from a system at NCSA (University of Illinois).
fido
with password bones
. Important Note:
There is no correspondence between usernames and
passwords on specific Unix systems (e.g. in an /etc/passwd
file) and usernames and passwords in the authentication
schemes we're discussing for use in the Web. As
illustrated in the examples, Web-based authentication
uses similar but wholly distinct password files; a
user need never have an actual account on a given Unix
system in order to be validated for access to files being
served from that system and protected with HTTP-based
authentication.
rover
with password bacon
and user jumpy
with password kibbles
.141.142.103.*
. Note
for non-NCSA readers: The .htaccess
file
used in this case is as follows:
AuthUserFile /dev/null
AuthGroupFile /dev/null
AuthName ExampleAllowFromNCSA
AuthType Basic
<Limit GET>
order deny,allow
deny from all
allow from 141.142.103.
</Limit>
141.142.103.*
.
Note for NCSA readers: The .htaccess
file used in this case is as follows:
AuthUserFile /dev/null
AuthGroupFile /dev/null
AuthName ExampleDenyFromNCSA
AuthType Basic
<Limit GET>
order allow,deny
allow from all
deny from 141.142.103.
</Limit>
Use Full Path Names
When specifying the AuthUserFile
and AuthGroupFile
,
you must use the full path name on the web server. I.e. use
"AuthUserFile /home/corp/johndoe/.htpasswd
"
not "AuthUserFile .htpasswd
".
Use the IP Address not the Domain Name
The Why? InterNetworking web server does not resolve the domain names of the
computers connecting to it. As a result, when using allow
from
or deny from
directives, you must use
the IP address.