Using Kerberos Authentication

Using Kerberos Authentication

You can control access to Greenplum Database with a Kerberos authentication server.

Greenplum Database supports the Generic Security Service Application Program Interface (GSSAPI) with Kerberos authentication. GSSAPI provides automatic authentication (single sign-on) for systems that support it. You specify the Greenplum Database users (roles) that require Kerberos authentication in the Greenplum Database configuration file pg_hba.conf. The login fails if Kerberos authentication is not available when a role attempts to log in to Greenplum Database.

Kerberos provides a secure, encrypted authentication service. It does not encrypt data exchanged between the client and database and provides no authorization services. To encrypt data exchanged over the network, you must use an SSL connection. To manage authorization for access to Greenplum databases and objects such as schemas and tables, you use settings in the pg_hba.conf file and privileges given to Greenplum Database users and roles within the database. For information about managing authorization privileges, see Managing Roles and Privileges.

For more information about Kerberos, see http://web.mit.edu/kerberos/.

Prerequisites

Before configuring Kerberos authentication for Greenplum Database, ensure that:

  • You can identify the KDC server you use for Kerberos authentication and the Kerberos realm for your Greenplum Database system.
    • If you plan to use an MIT Kerberos KDC server but have not yet configured it, see Installing and Configuring a Kerberos KDC Server for example instructions.
    • If you are using an existing Active Directory KDC server, also ensure that you have:
      • Installed all Active Directory service roles on your AD KDC server.
      • Enabled the LDAP service.
  • System time on the Kerberos Key Distribution Center (KDC) server and Greenplum Database master is synchronized. (For example, install the ntp package on both servers.)
  • Network connectivity exists between the KDC server and the Greenplum Database master host.
  • Java 1.7.0_17 or later is installed on all Greenplum Database hosts. Java 1.7.0_17 is required to use Kerberos-authenticated JDBC on Red Hat Enterprise Linux 6.x or 7.x.

Creating Greenplum Database Principals in the KDC Database

Create a service principal for the Greenplum Database service and a Kerberos admin principal that allows managing the KDC database as the gpadmin user.

  1. Log in to the Kerberos KDC server as the root user.
    $ ssh root@<kdc-server>
  2. Create a principal for the Greenplum Database service.
    # kadmin.local -q "addprinc -randkey postgres/mdw@GPDB.KRB"

    The -randkey option prevents the command from prompting for a password.

    The postgres part of the principal names matches the value of the Greenplum Database krb_srvname server configuration parameter, which is postgres by default.

    The host name part of the principal name must match the output of the hostname command on the Greenplum Database master host. If the hostname command shows the fully qualified domain name (FQDN), use it in the principal name, for example postgres/mdw.example.com@GPDB.KRB.

    The GPDB.KRB part of the principal name is the Kerberos realm name.

  3. Create a principal for the gpadmin/admin role.
    # kadmin.local -q "addprinc gpadmin/admin@GPDB.KRB"
    This principal allows you to manage the KDC database when you are logged in as gpadmin. Make sure that the Kerberos kadm.acl configuration file contains an ACL to grant permissions to this principal. For example, this ACL grants all permissions to any admin user in the GPDB.KRB realm.
    */admin@GPDB.KRB *
  4. Create a keytab file with kadmin.local. The following example creates a keytab file gpdb-kerberos.keytab in the current directory with authentication information for the Greenplum Database service principal and the gpadmin/admin principal.
    # kadmin.local -q "ktadd -k gpdb-kerberos.keytab postgres/mdw@GPDB.KRB gadmin/admin@GPDB.KRB"
  5. Copy the keytab file to the master host.
    # scp gpdb-kerberos.keytab gpadmin@mdw:~

Installing the Kerberos Client on the Master Host

Install the Kerberos client utilities and libraries on the Greenplum Database master.

  1. Install the Kerberos packages on the Greenplum Database master.
    $ sudo yum install krb5-libs krb5-workstation
  2. Copy the /etc/krb5.conf file from the KDC server to /etc/krb5.conf on the Greenplum Master host.

Configuring Greenplum Database to use Kerberos Authentication

Configure Greenplum Database to use Kerberos.

  1. Log in to the Greenplum Database master host as the gpadmin user.
    $ ssh gpadmin@<master>
    $ source /usr/local/greenplum-db/greenplum_path.sh
  2. Set the ownership and permissions of the keytab file you copied from the KDC server.
    $ chown gpadmin:gpadmin /home/gpadmin/gpdb-kerberos.keytab
    $ chmod 400 /home/gpadmin/gpdb-kerberos.keytab
  3. Configure the location of the keytab file by setting the Greenplum Database krb_server_keyfile server configuration parameter. This gpconfig command specifies the folder /home/gpadmin as the location of the keytab file gpdb-kerberos.keytab.
    $ gpconfig -c krb_server_keyfile -v  '/home/gpadmin/gpdb-kerberos.keytab'
  4. Modify the Greenplum Database file pg_hba.conf to enable Kerberos support. For example, adding the following line to pg_hba.conf adds GSSAPI and Kerberos authentication support for connection requests from all users and hosts on the same network to all Greenplum Database databases.
    host all all 0.0.0.0/0 gss include_realm=0 krb_realm=GPDB.KRB

    Setting the krb_realm option to a realm name ensures that only users from that realm can successfully authenticate with Kerberos. Setting the include_realm option to 0 excludes the realm name from the authenticated user name. For information about the pg_hba.conf file, see The pg_hba.conf file in the Postgres documentation.

  5. Restart Greenplum Database after updating the krb_server_keyfile parameter and the pg_hba.conf file.
    $ gpstop -ar
  6. Create the gpadmin/admin Greenplum Database superuser role.
    $ createuser gpadmin/admin
    Shall the new role be a superuser? (y/n) y

    The Kerberos keys for this database role are in the keyfile you copied from the KDC server.

  7. Create a ticket using kinit and show the tickets in the Kerberos ticket cache with klist.
    $ LD_LIBRARY_PATH= kinit -k -t /home/gpadmin/gpdb-kerberos.keytab gpadmin/admin@GPDB.KRB
    $ LD_LIBRARY_PATH= klist
    Ticket cache: FILE:/tmp/krb5cc_1000
    Default principal: gpadmin/admin@GPDB.KRB
    
    Valid starting       Expires              Service principal
    06/13/2018 17:37:35  06/14/2018 17:37:35  krbtgt/GPDB.KRB@GPDB.KRB
    Note: When you set up the Greenplum Database environment by sourcing the greenplum-db_path.sh script, the LD_LIBRARY_PATH environment variable is set to include the Greenplum Database lib directory, which includes Kerberos libraries. This may cause Kerberos utility commands such as kinit and klist to fail due to version conflicts. The solution is to run Kerberos utilities before you source the greenplum-db_path.sh file or temporarily unset the LD_LIBRARY_PATH variable when you execute Kerberos utilities, as shown in the example.
  8. As a test, log in to the postgres database with the gpadmin/admin role:
    $ psql -U "gpadmin/admin" -h mdw postgres
    psql (8.3.23)
    Type "help" for help.
    
    postgres=# select current_user;
     current_user
    ---------------
     gpadmin/admin
    (1 row)
    Note: When you start psql on the master host, you must include the -h <master-hostname> option to force a TCP connection because Kerberos authentication does not work with local connections.
If a Kerberos principal is not a Greenplum Database user, a message similar to the following is displayed from the psql command line when the user attempts to log in to the database:
psql: krb5_sendauth: Bad response

The principal must be added as a Greenplum Database user.

Mapping Kerberos Principals to Greenplum Database Roles

To connect to a Greenplum Database system with Kerberos authentication enabled, a user first requests a ticket-granting ticket from the KDC server using the kinit utility with a password or a keytab file provided by the Kerberos admin. When the user then connects to the Kerberos-enabled Greenplum Database system, the user's Kerberos principle name will be the Greenplum Database role name, subject to transformations specified in the options field of the gss entry in the Greenplum Database pg_hba.conf file:

  • If the krb_realm=<realm> option is present, Greenplum Database only accepts Kerberos principals who are members pf the specified realm.
  • If the include_realm=0 option is specified, the Greenplum Database role name is the Kerberos principal name without the Kerberos realm. If the include_realm=1 option is instead specified, the Kerberos realm is not stripped from the Greenplum Database rolename. The role must have been created with the Greenplum Database CREATE ROLE command.
  • If the map=<map-name> option is specified, the Kerberos principal name is compared to entries labeled with the specified <map-name> in the $MASTER_DATA_DIRECTORY/pg_ident.conf file and replaced with the Greenplum Database role name specified in the first matching entry.

A user name map is defined in the $MASTER_DATA_DIRECTORY/pg_ident.conf configuration file. This example defines a map named mymap with two entries.

# MAPNAME   SYSTEM-USERNAME        GP-USERNAME
mymap       /^admin@GPDB.KRB$      gpadmin
mymap       /^(.*)_gp)@GPDB.KRB$   \1

The map name is specified in the pg_hba.conf Kerberos entry in the options field:

host all all 0.0.0.0/0 gss include_realm=0 krb_realm=GPDB.KRB map=mymap

The first map entry matches the Kerberos principal admin@GPDB.KRB and replaces it with the Greenplum Database gpadmin role name. The second entry uses a wildcard to match any Kerberos principal in the GPDB-KRB realm with a name ending with the characters _gp and replaces it with the initial portion of the principal name. Greenplum Database applies the first matching map entry in the pg_ident.conf file, so the order of entries is significant.

For more information about using username maps see Username maps in the PostgreSQL documentation.

Configuring JDBC Kerberos Authentication for Greenplum Database

Enable Kerberos-authenticated JDBC access to Greenplum Database.

You can configure Greenplum Database to use Kerberos to run user-defined Java functions.

  1. Ensure that Kerberos is installed and configured on the Greenplum Database master. See Installing the Kerberos Client on the Master Host.

  2. Create the file .java.login.config in the folder /home/gpadmin and add the following text to the file:

    pgjdbc {
      com.sun.security.auth.module.Krb5LoginModule required
      doNotPrompt=true
      useTicketCache=true
      debug=true
      client=true;
    };
  3. Create a Java application that connects to Greenplum Database using Kerberos authentication. The following example database connection URL uses a PostgreSQL JDBC driver and specifies parameters for Kerberos authentication:

    jdbc:postgresql://mdw:5432/mytest?kerberosServerName=postgres
    &jaasApplicationName=pgjdbc&user=gpadmin/gpdb-kdc

    The parameter names and values specified depend on how the Java application performs Kerberos authentication.

  4. Test the Kerberos login by running a sample Java application from Greenplum Database.

Installing and Configuring a Kerberos KDC Server

Steps to set up a Kerberos Key Distribution Center (KDC) server on a Red Hat Enterprise Linux host for use with Greenplum Database.

If you do not already have a KDC, follow these steps to install and configure a KDC server on a Red Hat Enterprise Linux host with a GPDB.KRB realm. The host name of the KDC server in this example is gpdb-kdc.

  1. Install the Kerberos server and client packages:
    $ sudo yum install krb5-libs krb5-server krb5-workstation
  2. Edit the /etc/krb5.conf configuration file. The following example shows a Kerberos server configured with a default GPDB.KRB realm.
    [logging]
     default = FILE:/var/log/krb5libs.log
     kdc = FILE:/var/log/krb5kdc.log
     admin_server = FILE:/var/log/kadmind.log
    
    [libdefaults]
     default_realm = GPDB.KRB
     dns_lookup_realm = false
     dns_lookup_kdc = false
     ticket_lifetime = 24h
     renew_lifetime = 7d
     forwardable = true
     default_tgs_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
     default_tkt_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
     permitted_enctypes = aes128-cts des3-hmac-sha1 des-cbc-crc des-cbc-md5
    
    [realms]
     GPDB.KRB = {
      kdc = gpdb-kdc:88
      admin_server = gpdb-kdc:749
      default_domain = gpdb.krb
     }
    
    [domain_realm]
     .gpdb.krb = GPDB.KRB
     gpdb.krb = GPDB.KRB
    
    [appdefaults]
     pam = {
        debug = false
        ticket_lifetime = 36000
        renew_lifetime = 36000
        forwardable = true
        krb4_convert = false
     }
    

    The kdc and admin_server keys in the [realms] section specify the host (gpdb-kdc) and port where the Kerberos server is running. IP numbers can be used in place of host names.

    If your Kerberos server manages authentication for other realms, you would instead add the GPDB.KRB realm in the [realms] and [domain_realm] section of the kdc.conf file. See the Kerberos documentation for information about the kdc.conf file.

  3. To create the Kerberos database, run the kdb5_util.
    # kdb5_util create -s

    The kdb5_util create command creates the database to store keys for the Kerberos realms that are managed by this KDC server. The -s option creates a stash file. Without the stash file, every time the KDC server starts it requests a password.

  4. Add an administrative user to the KDC database with the kadmin.local utility. Because it does not itself depend on Kerberos authentication, the kadmin.local utility allows you to add an initial administrative user to the local Kerberos server. To add the user gpadmin as an administrative user to the KDC database, run the following command:
    # kadmin.local -q "addprinc gpadmin/admin"

    Most users do not need administrative access to the Kerberos server. They can use kadmin to manage their own principals (for example, to change their own password). For information about kadmin, see the Kerberos documentation.

  5. If needed, edit the /var/kerberos/krb5kdc/kadm5.acl file to grant the appropriate permissions to gpadmin.
  6. Start the Kerberos daemons:
    # /sbin/service krb5kdc start#
    /sbin/service kadmin start
  7. To start Kerberos automatically upon restart:
    # /sbin/chkconfig krb5kdc on
    # /sbin/chkconfig kadmin on