Apache Module mod_auth_digest

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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 (RFC2617), and provides an alternative to mod_auth_basic where the password is not transmitted as cleartext. However, this does not lead to a significant security advantage over basic authentication. On the other hand, the password storage on the server is much less secure with digest authentication than with basic authentication. Therefore, using basic auth and encrypting the whole connection using mod_ssl is a much better alternative.

Topics

Using Digest Authentication

Using Digest Authentication

To use MD5 Digest authentication, simply change the normal AuthType Basic and AuthBasicProvider to AuthType Digest and AuthDigestProvider, when setting up authentication, 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 was intended to be more secure than basic authentication, but no longer fulfills that design goal. A man-in-the-middle attacker can trivially force the browser to downgrade to basic authentication. And even a passive eavesdropper can brute-force the password using today's graphics hardware, because the hashing algorithm used by digest authentication is too fast. Another problem is that the storage of the passwords on the server is insecure. The contents of a stolen htdigest file can be used directly for digest authentication. Therefore using mod_ssl to encrypt the whole connection is strongly recommended.

mod_auth_digest only works properly on platforms where APR supports shared memory.

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, mod_authn_dbd and mod_authn_socache 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 dependent 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 follow the number with 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