Apache Module mod_auth_basic

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 bymod_auth_digest. This module should usually be combined with at least one authentication module such asmod_authn_file and one authorization module such asmod_authz_user.

Directives

• AuthBasicAuthoritative
• AuthBasicFake
• AuthBasicProvider
• AuthBasicUseDigestAlgorithm

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• AuthName
• AuthType
• Require
• Authentication howto
• Comments

AuthBasicAuthoritativeDirective

Normally, each authorization module listed inAuthBasicProvider will attempt to verify the user, and if the user is not found in any provider, access will be denied. Setting theAuthBasicAuthoritative directive explicitly toOff allows for both authentication and authorization to be passed on to other non-provider-based modules if there isno userID orrule matching the supplied userID. This should only be necessary when combiningmod_auth_basic with third-party modules that are not configured with theAuthBasicProvider directive. When using such modules, the order of processing is determined in the modules' source code and is not configurable.

AuthBasicFakeDirective

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 theexpression 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.

<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 theSSLOptions directive. Like the FakeBasicAuth option, the password is set to the fixed string "password".

<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.

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

<Location "/public">    AuthBasicFake off</Location>

AuthBasicProviderDirective

TheAuthBasicProvider directive sets which provider is used to authenticate the users for this location. The defaultfile provider is implemented by themod_authn_file module. Make sure that the chosen provider module is present in the server.

<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 bymod_authn_dbm,mod_authn_file,mod_authn_dbd,mod_authnz_ldap andmod_authn_socache.

AuthBasicUseDigestAlgorithmDirective

Normally, when using Basic Authentication, the providers listed inAuthBasicProvider 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 usingAuthDigestProvider 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 theAuthBasicUseDigestAlgorithm directive toMD5 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 inAuthBasicProvider as ifAuthType was set toDigest and Digest Authentication was in force.

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