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 for testing purposes, running the [login, password] authentication through the PAM stack.
The primary intended use is in connection with sssd and pam_sss.so.
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
and
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
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
By default the redirect is done using 303 See Other. The redirect status can be specified as numerical value in the 3xx range.
SELinux:
On SELinux enabled systems, boolean httpd_mod_auth_pam needs to be enabled:
setsebool -P httpd_mod_auth_pam 1
When building from sources, command
apxs -i -a -c mod_authnz_pam.c -lpam -Wall -pedantic
should build and install the module.
Copyright 2014--2022 Jan Pazdziora
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.