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Apache > HTTP Server > Documentation > Version 2.5 > Modules

Apache Module mod_auth_basic

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Description:Basic HTTP authentication
Status:Base
Module Identifier:auth_basic_module
Source File:mod_auth_basic.c

Summary

This module allows the use of HTTP Basic Authentication to restrict access by looking up users in the given providers. HTTP Digest Authentication is provided by mod_auth_digest. This module should usually be combined with at least one authentication module such as mod_authn_file and one authorization module such as mod_authz_user.

Directives

See also

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AuthBasicAuthoritative Directive

Description:Sets whether authorization and authentication are passed to lower level modules
Syntax:AuthBasicAuthoritative On|Off
Default:AuthBasicAuthoritative On
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_basic

Normally, each authorization module listed in AuthBasicProvider will attempt to verify the user, and if the user is not found in any provider, access will be denied. Setting the AuthBasicAuthoritative directive explicitly to Off allows for both authentication and authorization to be passed on to other non-provider-based modules if there is no userID or rule matching the supplied userID. This should only be necessary when combining mod_auth_basic with third-party modules that are not configured with the AuthBasicProvider directive. When using such modules, the order of processing is determined in the modules' source code and is not configurable.

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AuthBasicFake Directive

Description:Fake basic authentication using the given expressions for username and password
Syntax:AuthBasicFake off|username [password]
Default:none
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_basic

The username and password specified are combined into an Authorization header, which is passed to the server or service behind the webserver. Both the username and password fields are interpreted using the expression parser, which allows both the username and password to be set based on request parameters.

If the password is not specified, the default value "password" will be used. To disable fake basic authentication for an URL space, specify "AuthBasicFake off".

In this example, we pass a fixed username and password to a backend server.

Fixed Example

<Location /demo>
    AuthBasicFake demo demopass
</Location>

In this example, we pass the email address extracted from a client certificate, extending the functionality of the FakeBasicAuth option within the SSLOptions directive. Like the FakeBasicAuth option, the password is set to the fixed string "password".

Certificate Example

<Location /secure>
    AuthBasicFake %{SSL_CLIENT_S_DN_Email}
</Location>

Extending the above example, we generate a password by hashing the email address with a fixed passphrase, and passing the hash to the backend server. This can be used to gate into legacy systems that do not support client certificates.

Password Example

<Location /secure>
    AuthBasicFake %{SSL_CLIENT_S_DN_Email} %{sha1:passphrase-%{SSL_CLIENT_S_DN_Email}}
</Location>

Exclusion Example

<Location /public>
    AuthBasicFake off
</Location>
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AuthBasicProvider Directive

Description:Sets the authentication provider(s) for this location
Syntax:AuthBasicProvider provider-name [provider-name] ...
Default:AuthBasicProvider file
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_basic

The AuthBasicProvider 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.

Example

<Location /secure>
    AuthType basic
    AuthName "private area"
    AuthBasicProvider  dbm
    AuthDBMType        SDBM
    AuthDBMUserFile    /www/etc/dbmpasswd
    Require            valid-user
</Location>

Providers are queried in order until a provider finds a match for the requested username, at which point this sole provider will attempt to check the password. A failure to verify the password does not result in control being passed on to subsequent providers.

Providers are implemented by mod_authn_dbm, mod_authn_file, mod_authn_dbd, mod_authnz_ldap and mod_authn_socache.

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AuthBasicUseDigestAlgorithm Directive

Description:Check passwords against the authentication providers as if Digest Authentication was in force instead of Basic Authentication.
Syntax:AuthBasicUseDigestAlgorithm MD5|Off
Default:AuthBasicUseDigestAlgorithm Off
Context:directory, .htaccess
Override:AuthConfig
Status:Base
Module:mod_auth_basic

Normally, when using Basic Authentication, the providers listed in AuthBasicProvider attempt to verify a user by checking their data stores for a matching username and associated password. The stored passwords are usually encrypted, but not necessarily so; each provider may choose its own storage scheme for passwords.

When using AuthDigestProvider and Digest Authentication, providers perform a similar check to find a matching username in their data stores. However, unlike in the Basic Authentication case, the value associated with each stored username must be an encrypted string composed from the username, realm name, and password. (See RFC 2617, Section 3.2.2.2 for more details on the format used for this encrypted string.)

As a consequence of the difference in the stored values between Basic and Digest Authentication, converting from Digest Authentication to Basic Authentication generally requires that all users be assigned new passwords, as their existing passwords cannot be recovered from the password storage scheme imposed on those providers which support Digest Authentication.

Setting the AuthBasicUseDigestAlgorithm directive to MD5 will cause the user's Basic Authentication password to be checked using the same encrypted format as for Digest Authentication. First a string composed from the username, realm name, and password is hashed with MD5; then the username and this encrypted string are passed to the providers listed in AuthBasicProvider as if AuthType was set to Digest and Digest Authentication was in force.

Through the use of AuthBasicUseDigestAlgorithm a site may switch from Digest to Basic Authentication without requiring users to be assigned new passwords.

The inverse process of switching from Basic to Digest Authentication without assigning new passwords is generally not possible. Only if the Basic Authentication passwords have been stored in plain text or with a reversable encryption scheme will it be possible to recover them and generate a new data store following the Digest Authentication password storage scheme.
Only providers which support Digest Authentication will be able to authenticate users when AuthBasicUseDigestAlgorithm is set to MD5. Use of other providers will result in an error response and the client will be denied access.

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