Mosaic User Authentication Tutorial

Introduction

So basically this method of authentication is roughly as safe as telnet-style username and password security -- if you trust your machine to be on the Internet, open to attempts to telnet in by anyone who wants to try, then you have no reason not to trust this method also.

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 Unix^TM security model.

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 /otherdir/.htpasswd
AuthGroupFile /dev/null
AuthName ByPassword
AuthType Basic

<Limit GET>
require user pumpkin
</Limit>

Note that the password file will be in another directory (/otherdir).

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 for NCSA HTTPd 1.5 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>

Create the password file /otherdir/.htpasswd

The easiest way to do this is to use the htpasswd program distributed with NCSA HTTPd. Do this:

htpasswd -c /otherdir/.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.

Add additional users to the directory's .htpasswd file.

Use the htpasswd command without the -c flag to add additional users; e.g.:

htpasswd /otherdir/.htpasswd peanuts
htpasswd /otherdir/.htpasswd almonds
htpasswd /otherdir/.htpasswd walnuts

Create a group file.

Call it /otherdir/.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 /otherdir/.htpasswd
AuthGroupFile /otherdir/.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.