Apache module mod_authnz_pam

Apache module mod_authnz_pam serves as PAM authorization module, supplementing authentication done by other modules, for example mod_auth_kerb. It can also be used as a full Basic Authentication provider, running the [login, password] authentication through the PAM stack.

The primary intended use is in connection with SSSD and pam_sss.so but any PAM service with any PAM stack configuration for auth and account management groups can be used.

Download mod_authnz_pam-1.2.3.tar.gz, the latest release. See the source at either GitHub or fedorapeople.org.

Authorization

Let us assume there is already Kerberos authentication configured:

<Location /private>
  AuthType Kerberos
  AuthName "Kerberos Login"
  KrbMethodNegotiate On
  KrbMethodK5Passwd Off
  KrbAuthRealms EXAMPLE.COM
  Krb5KeyTab /etc/http.keytab
  KrbLocalUserMapping On
  Require valid-user
</Location>

The Require valid-user line can be replaced by

  Require pam-account pam_service_name

for example to run authorization check for the Kerberos-authenticated user using the PAM service pam_service_name.

This can be useful to get for example host-based access control from an IPA server for the web service.

Basic Authentication

The module is configured using the

AuthBasicProvider PAM

directive and then by specifying the PAM service name:

AuthPAMService name_of_the_PAM_service: The PAM service to authenticate against.

Example:

<Location /private>
  AuthType Basic
  AuthName "private area"
  AuthBasicProvider PAM
  AuthPAMService tlwiki
  Require valid-user
</Location>

The PAM service needs to be configured. For the above shown tlwiki example, file /etc/pam.d/tlwiki could be created with content

auth    required   pam_sss.so
account required   pam_sss.so

to authenticate against sssd.

As part of the Basic Authentication operation, both PAM authentication and PAM account verification (auth and account in PAM service configuration) are run. This is to ensure that the HTTP status 401 is returned when the user is not permitted to log in, allowing fallback to different authentication mechanism. That also means that for the above example

AuthBasicProvider PAM
AuthPAMService tlwiki

it is not necessary to use

Require pam-account tlwiki

since

Require valid-user

is enough because the account verification will be run as part of the HTTP authentication. In fact, using Require pam-account with the same PAM service name will cause the account PAM checks to be run twice. On the other hand, it is possible to configure Require pam-account with different PAM service name than the AuthPAMService value and get two separate account PAM checks during the Basic Authentication.

Handling expired password

AuthPAMExpiredRedirect <URL> [<status>]

For both the authorization and HTTP Basic authentication case, if the password the user has presented has expired (PAM return codes PAM_CRED_EXPIRED or PAM_NEW_AUTHTOK_REQD), when AuthPAMExpiredRedirect is specified with a URL, redirect is made to that location. For FreeIPA server, the setting would be

AuthPAMExpiredRedirect https://<IPA-server>/ipa/ui/reset_password.html

By default the redirect is done using 303 See Other. The redirect status can be specified as numerical value in the 3xx range.

It is also possible to use placeholders in the URL that will be replaced with current location (for backreference) and username (to prefill) on the target page:

%s: URL of the current page.
%u: The username that was used for the PAM authentication.
%%: The character % itself.

For example for FreeIPA 4.1+, the value can actually be

    https://<IPA-server>/ipa/ui/reset_password.html?url=%s

SELinux

On SELinux enabled systems, boolean httpd_mod_auth_pam needs to be enabled:

setsebool -P httpd_mod_auth_pam 1

Building from sources

When building from sources, command

apxs -i -a -c mod_authnz_pam.c -lpam -Wall -pedantic

should build and install the module.

License

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.