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Securing Your Web Pages with Apache Page 5




Since the username and password are so trivially protected in the
Basic authentication mechanism, the same authentication database can
be used to store user information for multiple realms. The
Digest mechanism, though, includes an encoding of the realm for
which the credentials are valid, so you must have a separate
credentials database for each realm using the Digest method.

When setting up discretionary controls in your Apache configuration,
remember that the AuthType directive is
required. The setting can be inherited from a higher-level
directory or location, but something must set the value to be
inherited; there is no default.

Mixing Mandatory and Discretionary Controls — The
Satisfy Directive

Sometimes you want to mix and match discretionary and non-discretionary
access controls, such as allowing anyone on the local network to
see documents freely, but requiring anyone else to enter a username
and password.

This can be done with the Satisfy directive, which takes
a single keyword:

All
In order to gain access to documents within the scope of a
Satisfy All directive, a client must
pass both any applicable non-discretionary controls (such
as Allow or Deny directives) and
any discretionary ones (like Require directives).
Any
Documents within the scope of a Satisfy Any
directive are accessible to any clients that either pass the
non-discretionary check (which occur first) or the
discretionary ones

To illustrate, the following would permit any client on the
local network (IP addresses 10.*.*.*) to access the foo.html
page without let or hindrance, but require a username and password
for anyone else:

  
    
        Order Deny,Allow
        Deny from All
        Allow from 10.0.0.0/255.0.0.0
        AuthName "Insiders Only"
        AuthType Basic
        AuthUserFile /usr/local/web/apache/.htpasswd-foo
        Require valid-user
        Satisfy Any
    

Restricting by IP Address

Since the IP address is one of those aspects of a client-server
HTTP relationship that cannot be changed mid-stream, and cannot
be easily faked (without the cooperation of the intervening
network systems), it's considered a non-discretionary control.
The Apache distribution includes a module for limiting access
thusly, called mod_access.

mod_access allows you to specify what domains
or addresses should or should not be allowed access, and in which order
the two lists (allowed and denied) should be evaluated. The basic
syntax of the Allow and Deny directives is

    Allow from host-or-network
  

The host-or-network can be:

  • a host or domain name (www.foo.com),
  • an IP address (10.0.72.3),
  • an IP address and subnet mask (10.0.0.0/255.0.0.0), or
  • an IP address and CIDR mask size (10.73.128.0/18)

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