Apache HTTP Server Version 2.5

Apache > HTTP Server > Documentation > Version 2.5 > Modules

# 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 (RFC 2617), 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

### Directives

### Bugfix checklist

- httpd changelog
- Known issues
- Report a bug

### See also

- `AuthName`
- `AuthType`
- `Require`
- Authentication howto

## Using Digest Authentication ¶

To use MD5 Digest authentication, configure the location to be protected as shown in the below example:

### 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>

`AuthDigestDomain` should list the locations that will be protected by this configuration.

The password file referenced in the `AuthUserFile` directive may be created and managed using the `htdigest` tool.

### 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