Apache2 Module mod_auth_digest


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.

Directives
  • AuthDigestAlgorithm
  • AuthDigestDomain
  • AuthDigestFile
  • AuthDigestGroupFile
  • AuthDigestNcCheck
  • AuthDigestNonceFormat
  • AuthDigestNonceLifetime
  • AuthDigestQop
  • AuthDigestShmemSize

    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> 
    Usage htdigest

    htdigest [-c] passwordfile realm username
    -c -- creates a new file.
    passwordfile -- outfile to contain the username, realm and password
    realm -- the realm name to which the user name belongs.
    username -- user naem to create or update in passwordfile .

    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 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 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. 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.

    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.