Authentication, Authorization and Access Control
Authentication is any process by which you verify that
someone is who they claim they are. Authorization is any
process by which someone is allowed to be where they want to
go, or to have information that they want to have.
For general access control, see the Access
There are three types of modules involved in the authentication and
authorization process. You will usually need to choose at least one
module from each group.
In addition to these modules, there are also
mod_authz_core. These module implement core
directives that are core to all auth modules.
mod_authnz_ldap is both an
authentication and authorization provider. The module
mod_authz_host provides authorization
and access control based on hostname, IP address or characteristics
of the request, but is not part of the authentication provider
system. For backwards compatibility with the mod_access, there is
a new module
You probably also want to take a look at the Access Control howto, which discusses the
various ways to control access to your server.
If you have information on your web site that is sensitive
or intended for only a small group of people, the techniques in
this article will help you make sure that the people that see
those pages are the people that you wanted to see them.
This article covers the "standard" way of protecting parts
of your web site that most of you are going to use.
If your data really needs to be secure, consider using
mod_ssl in addition to any authentication.
The directives discussed in this article will need to go
either in your main server configuration file (typically in a
<Directory> section), or
in per-directory configuration files (
If you plan to use
.htaccess files, you will
need to have a server configuration that permits putting
authentication directives in these files. This is done with the
AllowOverride directive, which
specifies which directives, if any, may be put in per-directory
Since we're talking here about authentication, you will need
AllowOverride directive like the
Or, if you are just going to put the directives directly in
your main server configuration file, you will of course need to
have write permission to that file.
And you'll need to know a little bit about the directory
structure of your server, in order to know where some files are
kept. This should not be terribly difficult, and I'll try to
make this clear when we come to that point.
You will also need to make sure that the modules
have either been built into the httpd binary or loaded by the
httpd.conf configuration file. Both of these modules provide core
directives and functionality that are critical to the configuration
and use of authentication and authorization in the web server.
Here's the basics of password protecting a directory on your
First, you need to create a password file. Exactly how you do
this will vary depending on what authentication provider you have
chosen. More on that later. To start with, we'll use a text password
This file should be
placed somewhere not accessible from the web. This is so that
folks cannot download the password file. For example, if your
documents are served out of
might want to put the password file(s) in
To create the file, use the
htpasswd utility that
came with Apache. This will be located in the
of wherever you installed Apache. If you have installed Apache from
a third-party package, it may be in your execution path.
To create the file, type:
htpasswd -c /usr/local/apache/passwd/passwords rbowen
htpasswd will ask you for the password, and
then ask you to type it again to confirm it:
# htpasswd -c /usr/local/apache/passwd/passwords rbowen
New password: mypassword
Re-type new password: mypassword
Adding password for user rbowen
htpasswd is not in your path, of course
you'll have to type the full path to the file to get it to run.
With a default installation, it's located at
Next, you'll need to configure the server to request a
password and tell the server which users are allowed access.
You can do this either by editing the
file or using an
.htaccess file. For example, if
you wish to protect the directory
/usr/local/apache/htdocs/secret, you can use the
following directives, either placed in the file
httpd.conf inside a <Directory
AuthName "Restricted Files"
# (Following line optional)
Require user rbowen
Let's examine each of those directives individually. The
AuthType directive selects
that method that is used to authenticate the user. The most
common method is
Basic, and this is the method
mod_auth_basic. It is important to be aware,
however, that Basic authentication sends the password from the client to
the server unencrypted. This method should therefore not be used for
highly sensitive data, unless accompanied by
Apache supports one other authentication method:
AuthType Digest. This method is implemented by
mod_auth_digest and is much more secure. Most recent
browsers support Digest authentication.
AuthName directive sets
the Realm to be used in the authentication. The realm serves
two major functions. First, the client often presents this information to
the user as part of the password dialog box. Second, it is used by the
client to determine what password to send for a given authenticated
So, for example, once a client has authenticated in the
"Restricted Files" area, it will automatically
retry the same password for any area on the same server that is
marked with the
"Restricted Files" Realm.
Therefore, you can prevent a user from being prompted more than
once for a password by letting multiple restricted areas share
the same realm. Of course, for security reasons, the client
will always need to ask again for the password whenever the
hostname of the server changes.
in this case, optional, since
file is the default value
for this directive. You'll need to use this directive if you are
choosing a different source for authentication, such as
directive sets the path to the password file that we just
htpasswd. If you have a large number
of users, it can be quite slow to search through a plain text
file to authenticate the user on each request. Apache also has
the ability to store user information in fast database files.
mod_authn_dbm module provides the
AuthDBMUserFile directive. These
files can be created and manipulated with the
dbmmanage program. Many
other types of authentication options are available from third
party modules in the Apache Modules
directive provides the authorization part of the process by
setting the user that is allowed to access this region of the
server. In the next section, we discuss various ways to use the
The directives above only let one person (specifically
someone with a username of
rbowen) into the
directory. In most cases, you'll want to let more than one
person in. This is where the
AuthGroupFile comes in.
If you want to let more than one person in, you'll need to
create a group file that associates group names with a list of
users in that group. The format of this file is pretty simple,
and you can create it with your favorite editor. The contents
of the file will look like this:
GroupName: rbowen dpitts sungo rshersey
That's just a list of the members of the group in a long
line separated by spaces.
To add a user to your already existing password file,
htpasswd /usr/local/apache/passwd/passwords dpitts
You'll get the same response as before, but it will be
appended to the existing file, rather than creating a new file.
-c that makes it create a new password
Now, you need to modify your
.htaccess file to
look like the following:
AuthName "By Invitation Only"
# Optional line:
Require group GroupName
Now, anyone that is listed in the group
and has an entry in the
password file, will be let in, if
they type the correct password.
There's another way to let multiple users in that is less
specific. Rather than creating a group file, you can just use
the following directive:
Using that rather than the
Require user rbowen
line will allow anyone in that is listed in the password file,
and who correctly enters their password. You can even emulate
the group behavior here, by just keeping a separate password
file for each group. The advantage of this approach is that
Apache only has to check one file, rather than two. The
disadvantage is that you have to maintain a bunch of password
files, and remember to reference the right one in the
Because of the way that Basic authentication is specified,
your username and password must be verified every time you
request a document from the server. This is even if you're
reloading the same page, and for every image on the page (if
they come from a protected directory). As you can imagine, this
slows things down a little. The amount that it slows things
down is proportional to the size of the password file, because
it has to open up that file, and go down the list of users
until it gets to your name. And it has to do this every time a
page is loaded.
A consequence of this is that there's a practical limit to
how many users you can put in one password file. This limit
will vary depending on the performance of your particular
server machine, but you can expect to see slowdowns once you
get above a few hundred entries, and may wish to consider a
different authentication method at that time.
Because storing passwords in plain text files has the above
problems, you may wish to store your passwords somewhere else, such
as in a database.
mod_authn_dbd are two
modules which make this possible. Rather than selecting
you can choose
dbd as your storage
To select a dbd file rather than a text file, for example:
Other options are available. Consult the
mod_authn_dbm documentation for more details.
With the introduction of the new provider based authentication and
authorization architecture, you are no longer locked into a single
authentication or authorization method. In fact any number of the
providers can be mixed and matched to provide you with exactly the
scheme that meets your needs. In the following example, both the
file and LDAP based authentication providers are being used.
AuthBasicProvider file ldap
In this example the file provider will attempt to authenticate
the user first. If it is unable to authenticate the user, the LDAP
provider will be called. This allows the scope of authentication
to be broadened if your organization implements more than
one type of authentication store. Other authentication and authorization
scenarios may include mixing one type of authentication with a
different type of authorization. For example, authenticating against
a password file yet authorizing against an LDAP directory.
Just as multiple authentication providers can be implemented, multiple
authorization methods can also be used. In this example both file group
authorization as well as LDAP group authorization is being used.
Require group GroupName
Require ldap-group cn=mygroup,o=yourorg
To take authorization a little further, authorization container
directives such as
allow logic to be applied so that the order in which authorization
is handled can be completely controled through the configuration.
Containers for an example of they may be applied.
The way that authorization can be apply is now much more flexible
than just a single check against a single data store. Ordering, logic
and choosing how authorization will be done is now possible.
Controling how and in what order authorization will be applied
has been a bit of a mystery in the past. In Apache 2.2 a provider-based
authentication mechanism was introduced to decouple the actual
authentication process from authorization and supporting functionality.
One of the side benefits was that authentication providers could be
configured and called in a specific order which didn't depend on the
load order of the auth module itself. This same provider based mechanism
has been brought forward into authorization as well. What this means is
not only specifies which authorization methods should be used, it also
specifies the order in which they are called. Multiple authorization
methods are called in the same order in which the
appear in the configuration.
With the introduction of authorization container directives
the configuration also has control over when the
authorization methods are called and what criteria determines when
access is granted. See
for an example of how they may be used to express complex
By default all
directives are handled as though contained within a
container directive. In other words, if
any of the specified authorization methods succeed, then authorization
Authentication by username and password is only part of the
story. Frequently you want to let people in based on something
other than who they are. Something such as where they are
The authorization providers
ip let you allow or deny access based other host based
criteria such as host name or ip address of the machine requesting
The usage of these providers is specified through the
This directive registers the authorization providers
that will be called during the authorization stage of the request
processing. For example:
where address is an IP address (or a partial IP
where domain_name is a fully qualified domain name
(or a partial domain name); you may provide multiple addresses or
domain names, if desired.
For example, if you have someone spamming your message
board, and you want to keep them out, you could do the
Require all granted
Require not ip 10.252.46.165
Visitors coming from that address will not be able to see
the content covered by this directive. If, instead, you have a
machine name, rather than an IP address, you can use that.
Require all granted
Require not host host.example.com
And, if you'd like to block access from an entire domain,
you can specify just part of an address or domain name:
Require all granted
Require ip 192.168.205
Require host phishers.example.com moreidiots.example
Require host ke
The above example uses the
to make sure that none of the
contained within it
match their parameters before granting access.
One of the side effects of adopting a provider based mechanism for
authentication is that the need for the previous access control directives
Satisfy are no longer needed.
However to provide backwards compatibility for older configurations, these
directives have been moved to the
There may be times when authentication puts an unacceptable load
on a provider or on your network. This is most likely to affect users
mod_authn_dbd (or third-party/custom providers).
To deal with this, HTTPD 2.3/2.4 introduces a new cacheing provider
mod_authn_socache to cache credentials and reduce
the load on the origin provider(s).
This may offer a substantial performance boost to some users.
You should also read the documentation for
contain some more information about how this all works.
can also help in simplifying certain authentication configurations.
The various ciphers supported by Apache for authentication data are
explained in Password
And you may want to look at the Access
Control howto, which discusses a number of related topics.