Apache Module mod_auth_digest

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Description:	User authentication using MD5 Digest Authentication.
Status:	Experimental
Module Identifier:	auth_digest_module
Source File:	mod_auth_digest.c

Summary

This module implements HTTP Digest Authentication. However, it has not been extensively tested and is therefore marked experimental.

Topics

Using Digest Authentication
Working with MS Internet Explorer

Using Digest Authentication

Using MD5 Digest authentication is very simple. Simply set up authentication normally, using AuthType Digest and AuthDigestFile instead of the normal AuthType Basic and AuthUserFile; also, replace any AuthGroupFile with AuthDigestGroupFile. 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/ AuthDigestFile /web/auth/.digest_pw Require valid-user </Location>

Note

Digest authentication provides a more secure password system than Basic authentication, but only works with supporting browsers. As of November 2002, the major browsers that support digest authentication are Opera, MS Internet Explorer (fails when used with a query string - see "Working with MS Internet Explorer" below for a workaround), Amaya, Mozilla and Netscape since version 7. Since digest authentication is not as widely implemented as basic authentication, you should use it only in controlled environments.

Working with MS Internet Explorer

The Digest authentication implementation in current Internet Explorer implementations has known issues, namely that GET requests with a query string are 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 request URI from the digest comparison. Using this method would look similar to the following.

Using Digest Authentication with MSIE:

BrowserMatch "MSIE" AuthDigestEnableQueryStringHack=On

See the BrowserMatch directive for more details on conditionally setting environment variables

AuthDigestAlgorithm Directive

Description:	Selects the algorithm used to calculate the challenge and response hases in digest authentication
Syntax:	`AuthDigestAlgorithm MD5\|MD5-sess`
Default:	`AuthDigestAlgorithm MD5`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

The AuthDigestAlgorithm directive selects the algorithm used to calculate the challenge and response hashes.

MD5-sess is not correctly implemented yet.

AuthDigestDomain Directive

Description:	URIs that are in the same protection space for digest authentication
Syntax:	`AuthDigestDomain URI [URI] ...`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

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, i.e. 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. inluding 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.

AuthDigestFile Directive

Description:	Location of the text file containing the list of users and encoded passwords for digest authentication
Syntax:	`AuthDigestFile file-path`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

The AuthDigestFile directive sets the name of a textual file containing the list of users and encoded passwords for digest authentication. File-path is the absolute path to the user file.

The digest file uses a special format. Files in this format can be created using the htdigest utility found in the support/ subdirectory of the Apache distribution.

AuthDigestGroupFile Directive

Description:	Name of the text file containing the list of groups for digest authentication
Syntax:	`AuthDigestGroupFile file-path`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

The AuthDigestGroupFile directive sets the name of a textual file containing the list of groups and their members (user names). File-path is the absolute path to the group file.

Each line of the group file contains a groupname followed by a colon, followed by the member usernames separated by spaces. Example:

mygroup: bob joe anne

Note that searching large text files is very inefficient.

Security:

Make sure that the AuthGroupFile is stored outside the document tree of the web-server; do not put it in the directory that it protects. Otherwise, clients may be able to download the AuthGroupFile.

AuthDigestNcCheck Directive

Description:	Enables or disables checking of the nonce-count sent by the server
Syntax:	`AuthDigestNcCheck On\|Off`
Default:	`AuthDigestNcCheck Off`
Context:	server config
Status:	Experimental
Module:	mod_auth_digest

Not implemented yet.

AuthDigestNonceFormat Directive

Description:	Determines how the nonce is generated
Syntax:	`AuthDigestNonceFormat format`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

Not implemented yet.

AuthDigestNonceLifetime Directive

Description:	How long the server nonce is valid
Syntax:	`AuthDigestNonceLifetime seconds`
Default:	`AuthDigestNonceLifetime 300`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

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.

AuthDigestQop Directive

Description:	Determines the quality-of-protection to use in digest authentication
Syntax:	`AuthDigestQop none\|auth\|auth-int [auth\|auth-int]`
Default:	`AuthDigestQop auth`
Context:	directory, .htaccess
Override:	AuthConfig
Status:	Experimental
Module:	mod_auth_digest

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

Description:	The amount of shared memory to allocate for keeping track of clients
Syntax:	`AuthDigestShmemSize size`
Default:	`AuthDigestShmemSize 1000`
Context:	server config
Status:	Experimental
Module:	mod_auth_digest

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 neccessary 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