Apache Module mod_auth_digest
Summary
This module implements HTTP Digest Authentication (RFC2617), and provides a more secure alternative to mod_auth_basic
.
Using Digest Authentication
Using MD5 Digest authentication is very simple. Simply set up authentication normally, using AuthType Digest
and AuthDigestProvider
instead of the normal AuthType Basic
and AuthBasicProvider
. Then add a AuthDigestDomain
directive containing at least the root URI(s) for this protection space.
Appropriate user (text) files can be created using the htdigest
tool.
Example:
<Location /private/>
AuthType Digest
AuthName "private area"
AuthDigestDomain /private/ http://mirror.my.dom/private2/
AuthDigestProvider file
AuthUserFile /web/auth/.digest_pw
Require valid-user
</Location>
Note
Digest authentication is more secure than Basic authentication, but only works with supporting browsers. As of September 2004, major browsers that support digest authentication include Amaya, Konqueror, MS Internet Explorer for Mac OS X and Windows (although the Windows version fails when used with a query string -- see "Working with MS Internet Explorer" below for a workaround), Mozilla, Netscape 7, Opera, and Safari. lynx does not support digest authentication. Since digest authentication is not as widely implemented as basic authentication, you should use it only in environments where all users will have supporting browsers.
Working with MS Internet Explorer
The Digest authentication implementation in previous Internet Explorer for Windows versions (5 and 6) had issues, namely that GET
requests with a query string were not RFC compliant. There are a few ways to work around this issue.
The first way is to use POST
requests instead of GET
requests to pass data to your program. This method is the simplest approach if your application can work with this limitation.
Since version 2.0.51 Apache also provides a workaround in the AuthDigestEnableQueryStringHack
environment variable. If AuthDigestEnableQueryStringHack
is set for the request, Apache will take steps to work around the MSIE bug and remove the query string from the digest comparison. Using this method would look similar to the following.
Using Digest Authentication with MSIE:
BrowserMatch "MSIE" AuthDigestEnableQueryStringHack=On
This workaround is not necessary for MSIE 7, though enabling it does not cause any compatibility issues or significant overhead.
See the BrowserMatch
directive for more details on conditionally setting environment variables.
AuthDigestAlgorithm Directive
The AuthDigestAlgorithm
directive selects the algorithm used to calculate the challenge and response hashes.
MD5-sess
is not correctly implemented yet.
AuthDigestDomain Directive
The AuthDigestDomain
directive allows you to specify one or more URIs which are in the same protection space (i.e. use the same realm and username/password info). The specified URIs are prefixes; the client will assume that all URIs "below" these are also protected by the same username/password. The URIs may be either absolute URIs (i.e. including a scheme, host, port, etc.) or relative URIs.
This directive should always be specified and contain at least the (set of) root URI(s) for this space. Omitting to do so will cause the client to send the Authorization header for every request sent to this server. Apart from increasing the size of the request, it may also have a detrimental effect on performance if AuthDigestNcCheck
is on.
The URIs specified can also point to different servers, in which case clients (which understand this) will then share username/password info across multiple servers without prompting the user each time.
AuthDigestNcCheck Directive
Not implemented yet.
AuthDigestNonceFormat Directive
Not implemented yet.
AuthDigestNonceLifetime Directive
The AuthDigestNonceLifetime
directive controls how long the server nonce is valid. When the client contacts the server using an expired nonce the server will send back a 401 with stale=true
. If seconds is greater than 0 then it specifies the amount of time for which the nonce is valid; this should probably never be set to less than 10 seconds. If seconds is less than 0 then the nonce never expires.
AuthDigestProvider Directive
The AuthDigestProvider
directive sets which provider is used to authenticate the users for this location. The default file
provider is implemented by the mod_authn_file
module. Make sure that the chosen provider module is present in the server.
See mod_authn_dbm
, mod_authn_file
, and mod_authn_dbd
for providers.
AuthDigestQop Directive
The AuthDigestQop
directive determines the quality-of-protection to use. auth
will only do authentication (username/password); auth-int
is authentication plus integrity checking (an MD5 hash of the entity is also computed and checked); none
will cause the module to use the old RFC-2069 digest algorithm (which does not include integrity checking). Both auth
and auth-int
may be specified, in which the case the browser will choose which of these to use. none
should only be used if the browser for some reason does not like the challenge it receives otherwise.
auth-int
is not implemented yet.
AuthDigestShmemSize Directive
The AuthDigestShmemSize
directive defines the amount of shared memory, that will be allocated at the server startup for keeping track of clients. Note that the shared memory segment cannot be set less than the space that is necessary for tracking at least one client. This value is dependant on your system. If you want to find out the exact value, you may simply set AuthDigestShmemSize
to the value of 0
and read the error message after trying to start the server.
The size is normally expressed in Bytes, but you may let the number follow a K
or an M
to express your value as KBytes or MBytes. For example, the following directives are all equivalent:
AuthDigestShmemSize 1048576
AuthDigestShmemSize 1024K
AuthDigestShmemSize 1M