Enabling Authentication with Kerberos

If you have enabled Kerberos authentication for Greenplum Database, you can set up Greenplum Command Center to accept connections from Kerberos-authenticated users.

Greenplum Database and Command Center include support for the Generic Security Service Applications Program Interface (GSS-API) standard. A related standard, Simple and Protected GSS-API Negotiation Mechanism (SPNEGO), describes the protocol GSS-API clients and servers use to agree on the method of authentication.

With a SPNEGO-compliant web application such as Command Center, the client and server agree on the authentication method on the client’s initial HTTP request. If Kerberos authentication is not supported on both ends of the connection the server falls back to basic authentication, and displays a login form requesting a user name and password. If a user has authenticated on the workstation with Kerberos and has a valid ticket granting ticket, the web browser offers the user’s credential to the Command Center web server. A Kerberos-enabled Command Center web server is configured to handle the authenticated user’s connection request in one of three modes, called strict, normal, or gpmon-only.

If you have set up Kerberos authentication for Greenplum Database, most of the configuration required to enable Command Center Kerberos authentication has been done. The Command Center Kerberos configuration builds upon the Greenplum Database Kerberos setup.

Kerberos authentication can be enabled by responding to prompts when you install Command Center, or you can use the gpcc --krbenable command to enable Kerberos after Command Center has been installed.

Before You Begin

Kerberos authentication must be enabled for Greenplum Database. See Using Kerberos Authentication for instructions. Make sure the following prerequisites are met before you continue:

• The krb5-workstation package and associated libraries (libkrb5*) must be installed on the Greenplum master host and each client workstation.
• The date and time on the Greenplum master host and all client workstations must be synchronized with the KDC.
• The krb5.conf configuration file must be the same on the KDC host, the Greenplum Database master host, and client workstations.
• The KDC database must have a service principal for Greenplum Database. The default service name for Greenplum Database is postgres/<master-host>@<realm>. You can choose a service name other than postgres, but it must match the value of the krb_srvname parameter in the $MASTER_DATA_DIRECTORY/postgresql.conf file.
• A keytab file with the Greenplum Database principal must be installed on the Greenplum master host and identified by the krb_server_keyfile parameter in the $MASTER_DATA_DIRECTORY/postgresql.conf file.
• Each client workstation can have a keytab file containing their Kerberos principal, <username>@<realm>.

Add Command Center Principals to the KDC Database

Before you configure Command Center for Kerberos authentication, you must create the required Kerberos principals. All of the principals used with Command Center are created in the Greenplum Database Kerberos realm. Command Center users can use the same Kerberos principal to authenticate with Command Center and Greenplum Database.

Adding Kerberos Principals

To add the required principals, perform the following steps as root on the KDC server.

1. Add a principal for the Command Center web service. Be sure to specify the <gpcc-host> in the same format that users should enter the host in their browsers.

   # kadmin.local -q "addprinc -randkey HTTP/<gpcc-host>@<realm>"
   

2. If you want the gpmon database user to use Kerberos authentication, add a gpmon principal.

   # kadmin.local -q "addprinc gpmon@<realm>"
   

3. Add principals for any new Command Center users.

   # kadmin.local -q "addprinc cc_user1@<realm>"
   

   Repeat for each new Command Center user.

Set Up Keytab Files

After you have created all of the Kerberos principals needed, you create and distribute keytab files. Keytab files contain Kerberos principals and encrypted keys based on the principals’ Kerberos passwords. Keytab files are needed for the Greenplum Database master and standby hosts and the Command Center host.

You can also create a keytab file for each Greenplum Database or Command Center user containing just the user’s principal. This keytab file is installed on the user’s workstation to enable the user to authenticate to Kerberos. Note that all keytab files must contain the most recent versions of the principals’ keys.

Command Center Running on the Greenplum Master Host

If the Greenplum Command Center web server is running on the Greenplum Database master host, Command Center can share the Greenplum Database keytab file. You need to create a keytab file that contains the following principals:

• Service key for the postgres process on the Greenplum Database master host, for example postgres/mdw.example.com@GPDB.EXAMPLE.
• Service key created for Command Center in the previous section, for example HTTP/mdw.example.com@GPDB.KRB.
• A principal for every Kerberos-authenticated Greenplum Database or Command Center user.

All service keys and principals should be in the Greenplum Database realm.

To create a keytab file for Greenplum Database and Command Center, perform the following steps as root on the KDC server.

1. Create a keytab file containing the Greeplum Database service key, the command center service key, and all database and Command Center users.

   kadmin.local -q "ktadd -k gpdb-kerberos.keytab postgres/mdw.example.com@GPDB.KRB HTTP/mdw.example.com@GPDB.KRB"
   

   You can enter one or more principals with each ktadd command. You can specify a wildcard using the -glob option. For example this command adds all principals in the GPDB.KRB realm, including service principals and admin users.

    kadmin.local -q "ktadd -k gpdb-kerberos.keytab -glob *@GPDB.KRB" 
   

2. Copy the keytab you created to the Greenplum Database master host, replacing the old keytab file. The location of the file is given by the krb_server_keyfile parameter in the $MASTER_DATA_FILE/postgresql.conf file. Set the permissions on the file so that it can be read only by the gpadmin user.

3. Update any entries required for new Greenplum Database principals in the pg_hba.conf file and pg_ident.conf files. See Update the Greenplum Database pg_hba.conf File for details.

Command Center Running on the Standby Master

If the Command Center web server is on a different host than the Greenplum Database master, you need separate keytab files for Greenplum Database and Command Center. The keytab file for Greenplum Database may not require any updates, but you will need to create a keytab file for Command Center.

• The Greenplum Database keytab file must contain the Greenplum Database service key and all principals for users with database access.
• The Command Center keytab file contains the Command Center service key and principals for users that have Command Center access. Users with Command Center access must also have Greenplum Database access, so user principals in the Command Center keytab file must also be in the Greenplum Database keytab file.

Update the Greenplum Database keytab if you created new database roles and principals for Command Center. For example, if you want to use Kerberos authentication for the gpmon user, you must create a principal and add it to both the Greenplum Database and Command Center keytab files.

To create the keytab file for Command Center, perform the following steps as root on the KDC host.

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1. Create a keytab file and add the Command Center service key.

   kadmin.local -q "ktadd -k gpcc-kerberos.keytab HTTP/smdw.example.com@GPDB.KRB"
   

2. If you want to authenticate the gpmon user with Kerberos, add the gpmon principal.

   kadmin.local -q "ktadd -k gpcc-kerberos.keytab gpmon@GPDB.KRB"
   

3. Add principals for all Command Center users:

   kadmin.local -q "ktadd -k gpcc-kerberos.keytab cc_user1@GPDB.KRB cc_user2@GPDB.KRB"
   

   You can enter one or more principals with each ktadd command.

4. Enter quit to exit kadmin.local.

5. Copy the keytab you created to the the host running Command Center, for example:

   $ scp gpcc-kerberos.keytab gpadmin@<host-name>:/home/gpadmin
   

6. Update any entries required for new principals in the pg_hba.conf file and pg_ident.conf files on the Greenplum master. See Update the Greenplum Database pg_hba.conf File.

Update the Greenplum Database pg_hba.conf File

The Greenplum Database $MASTER_DATA_DIRECTORY/pg_hba.conf configuration file determines which authentication methods to use to allow database access.

If you created new Command Center users, you may need to add an entry to allow access via Command Center. The entry for an individual user has this format:

host database <user-name> <gpcc CIDR> gss [options]

Authentication for the gpmon user needs to be set up in the pg_hba.conf file in one of the following ways.

local all gpmon md5

local all gpmon trust

host all gpmon <gpcc CIDR> gss [options]

host all gpmon <auth-method> reject

See Using Kerberos Authentication for more information about the pg_hba.conf file.

Enable Kerberos for Command Center

Set up Command Center to use the Command Center keytab file you created.

If you are adding Kerberos authentication to an existing Command Center, use the gpcc command. For example:

$ gpcc --krbenable

Enter the Command Center host name and path to the keytab file at the prompts. See the gpcc Reference for more information.

Authenticating With Kerberos on the Client Workstation

To use Kerberos Command Center authentication, the user must have authenticated with Kerberos using the kinit command-line tool.

The user then accesses the Command Center web server with a URL containing the host name in the format specified in the Command Center service principal and the port number, for example http://mdw.example.com:28080.

The user’s web browser must be configured to use the SPNEGO protocol so that it offers the user’s Kerberos principal to the web browser. The method for configuring web browsers varies with different browsers and operating systems. Search online to find instructions to enable SPNEGO with your browser and OS.