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Setting up PAM Authentication

PAM authentication is configured by adding a "ShiroProvider" authentication provider to the cluster's topology file with PAM parameters. When enabled, the Knox Gateway uses Apache Shiro and the parameter org.apache.hadoop.gateway.shirorealm.KnoxPamRealm to authenticate users against the configured PAM store.

About This Task

There are a large number of pluggable authentication modules available for authenticating access to Hadoop through the Knox Gateway. ShiroProvider, in addition to LDAP support, also includes support for PAM-based authentication for unix-based systems.

This opens up the integration possibilities to many other readily-available authentication mechanisms, as well as other implementations for LDAP-based authentication. More flexibility may be available through various PAM modules for group lookup, more complicated LDAP schemas, or other areas where the KnoxLdapRealm is not sufficient.

The primary motivation for leveraging PAM-based authentication is to provide the ability to use the configuration provided by existing PAM modules that are available in a system’s /etc/pam.d/ directory.

The parameter main.pamRealm.service refers to the service located in /etc/pam.d/login.

Steps

  1. In Ambari, add the ShiroProvider authentication provider to Knox>Configs>Advanced topology as follows:

    <provider> 
       <role>authentication</role> 
       <name>ShiroProvider</name> 
       <enabled>true</enabled> 
       <param> 
            <name>sessionTimeout</name> 
            <value>30</value>
        </param>                                              
        <param>
            <name>main.pamRealm</name> 
            <value>org.apache.hadoop.gateway.shirorealm.KnoxPamRealm</value>
        </param> 
        <param>                                                    
           <name>main.pamRealm.service</name> 
           <value>login</value> </param>
        <param>                                                    
           <name>urls./**</name> 
           <value>authcBasic</value> 
       </param>
    </provider>
  2. Save the file.

Example of a PAM Configuration File

The Shiro configuration above refers to the login file contained in /etc/pam.d. The configuration of the login file can be modified for your deployment:

# login: auth account password session
auth       optional       pam_krb5.so use_kcminit
auth       optional       pam_ntlm.so try_first_pass
auth       optional       pam_mount.so try_first_pass
auth       required       pam_opendirectory.so try_first_pass
account    required       pam_nologin.so
account    required       pam_opendirectory.so
password   required       pam_opendirectory.so
session    required       pam_launchd.so
session    required       pam_uwtmp.so
session    optional       pam_mount.so

The first four fields are: service-name, module-type, control-flag and module-filename. The fifth and greater fields are for optional arguments that are specific to the individual authentication modules.

The second field in the configuration file is the module-type, it indicates which of the four PAM management services the corresponding module will provide to the application. Our sample configuration file refers to all four groups:

  • auth: identifies the PAMs that are invoked when the application calls pam_authenticate() and pam_setcred().

  • account: maps to the pam_acct_mgmt() function.

  • session: indicates the mapping for the pam_open_session() and pam_close_session() calls.

  • password: group refers to the pam_chauthtok() function.

Generally, you only need to supply mappings for the functions that are needed by a specific application. For example, the standard password changing application, passwd, only requires a password group entry; any other entries are ignored.

The third field indicates what action is to be taken based on the success or failure of the corresponding module. Choices for tokens to fill this field are:

  • requisite: Failure instantly returns control to the application indicating the nature of the first module failure.

  • required: All these modules are required to succeed for libpam to return success to the application.

  • sufficient: Given that all preceding modules have succeeded, the success of this module leads to an immediate and successful return to the application (failure of this module is ignored).

  • optional: The success or failure of this module is generally not recorded.

The fourth field contains the name of the loadable module, pam_*.so. For the sake of readability, the full pathname of each module is not given. Before Linux-PAM-0.56 was released, there was no support for a default authentication-module directory. If you have an earlier version of Linux-PAM installed, you will have to specify the full path for each of the modules. Your distribution most likely placed these modules exclusively in one of the following directories: /lib/security/ or /usr/lib/security/.