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The Apache HTTP Server Reference Manual
by Apache Software Foundation
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ISBN 9781906966034
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3.8  Apache Module mod_auth_digest



Description:

User authentication using MD5 Digest Authentication.

Status:

Extension

Module Identifier:

auth_digest_module

Source File:

mod_auth_digest.c



Summary

This module implements HTTP Digest Authentication (RFC26178 ), and provides a more secure alternative to mod_auth_basic.

Directives:

AuthDigestAlgorithm

AuthDigestDomain

AuthDigestNcCheck

AuthDigestNonceFormat

AuthDigestNonceLifetime

AuthDigestProvider

AuthDigestQop

AuthDigestShmemSize

See also:

3.8.1  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 Amaya9 , Konqueror10 , MS Internet Explorer11 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), Mozilla12 , Netscape13 7, Opera14 , and Safari15 . lynx16 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.

3.8.2  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

Description:

Selects the algorithm used to calculate the challenge and response hashes in digest authentication

Syntax:

AuthDigestAlgorithm MD5|MD5-sess

Default:

AuthDigestAlgorithm MD5

Context:

directory, .htaccess

Override:

AuthConfig

Status:

Extension

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:

Extension

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; 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

Description:

Enables or disables checking of the nonce-count sent by the server

Syntax:

AuthDigestNcCheck On|Off

Default:

AuthDigestNcCheck Off

Context:

server config

Status:

Extension

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:

Extension

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:

Extension

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.

AuthDigestProvider Directive

Description:

Sets the authentication provider(s) for this location

Syntax:

AuthDigestProvider provider-name [provider-name]

Default:

AuthDigestProvider file

Context:

directory, .htaccess

Override:

AuthConfig

Status:

Extension

Module:

mod_auth_digest

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

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:

Extension

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:

Extension

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 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

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