19.6. GSSAPI Authentication
GSSAPI is an industry-standard protocol for secure authentication defined in RFC 2743. Postgres Pro supports GSSAPI with Kerberos authentication according to RFC 1964. GSSAPI provides automatic authentication (single sign-on) for systems that support it. The authentication itself is secure, but the data sent over the database connection will be sent unencrypted unless SSL is used.
GSSAPI support has to be enabled when Postgres Pro is built.
When GSSAPI uses Kerberos, it uses a standard principal in the format servicename/hostname@realmkrbsrvname connection parameter. (See also Section 32.1.2.) The installation default can be changed from the default postgres at build time using ./configure --with-krb-srvnam=whatever. In most environments, this parameter never needs to be changed. Some Kerberos implementations might require a different service name, such as Microsoft Active Directory which requires the service name to be in upper case (POSTGRES).
hostname is the fully qualified host name of the server machine. The service principal's realm is the preferred realm of the server machine.
Client principals can be mapped to different Postgres Pro database user names with pg_ident.conf. For example, pgusername@realm could be mapped to just pgusername. Alternatively, you can use the full username@realm principal as the role name in Postgres Pro without any mapping.
Postgres Pro also supports a parameter to strip the realm from the principal. This method is supported for backwards compatibility and is strongly discouraged as it is then impossible to distinguish different users with the same user name but coming from different realms. To enable this, set include_realm to 0. For simple single-realm installations, doing that combined with setting the krb_realm parameter (which checks that the principal's realm matches exactly what is in the krb_realm parameter) is still secure; but this is a less capable approach compared to specifying an explicit mapping in pg_ident.conf.
Make sure that your server keytab file is readable (and preferably only readable, not writable) by the Postgres Pro server account. (See also Section 17.1.) The location of the key file is specified by the krb_server_keyfile configuration parameter. The default is /usr/local/pgsql/etc/krb5.keytab (or whatever directory was specified as sysconfdir at build time). For security reasons, it is recommended to use a separate keytab just for the Postgres Pro server rather than opening up permissions on the system keytab file.
The keytab file is generated by the Kerberos software; see the Kerberos documentation for details. The following example is for MIT-compatible Kerberos 5 implementations:
kadmin%ank -randkey postgres/server.my.domain.orgkadmin%ktadd -k krb5.keytab postgres/server.my.domain.org
When connecting to the database make sure you have a ticket for a principal matching the requested database user name. For example, for database user name fred, principal fred@EXAMPLE.COM would be able to connect. To also allow principal fred/users.example.com@EXAMPLE.COM, use a user name map, as described in Section 19.2.
The following configuration options are supported for GSSAPI:
include_realmIf set to 0, the realm name from the authenticated user principal is stripped off before being passed through the user name mapping (Section 19.2). This is discouraged and is primarily available for backwards compatibility, as it is not secure in multi-realm environments unless
krb_realmis also used. It is recommended to leaveinclude_realmset to the default (1) and to provide an explicit mapping inpg_ident.confto convert principal names to Postgres Pro user names.mapAllows for mapping between system and database user names. See Section 19.2 for details. For a GSSAPI/Kerberos principal, such as
username@EXAMPLE.COM(or, less commonly,username/hostbased@EXAMPLE.COM), the user name used for mapping isusername@EXAMPLE.COM(orusername/hostbased@EXAMPLE.COM, respectively), unlessinclude_realmhas been set to 0, in which caseusername(orusername/hostbased) is what is seen as the system user name when mapping.krb_realmSets the realm to match user principal names against. If this parameter is set, only users of that realm will be accepted. If it is not set, users of any realm can connect, subject to whatever user name mapping is done.