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Chapter 33. Client Authentication
When a client application connects to the database server, it specifies which EnterpriseDB user name it wants to connect as, much the same way one logs into a Unix computer as a particular user. Within the SQL environment the active database user name determines access privileges to database objects - see Chapter 31 for more information. Therefore, it is essential to restrict which database users can connect. Authentication is the process by which the database server establishes the identity of the client, and by extension determines whether the client application (or the user who runs the client application) is permitted to connect with the user name that was requested. EnterpriseDB offers a number of different client authentication methods. The method used to authenticate a particular client connection can be selected on the basis of (client) host address, database, and user. EnterpriseDB user names are logically separate from user names of the operating system in which the server runs. If all the users of a particular server also have accounts on the server's machine, it makes sense to assign database user names that match their operating system user names. However, a server that accepts remote connections may have many database users who have no local operating system account, and in such cases there need be no connection between database user names and OS user names. 33.1. The pg_hba.conf fileClient authentication is controlled by the file pg_hba.conf in the data directory, e.g., /usr/local/gssql/data/pg_hba.conf. (HBA stands for host-based authentication.) A default pg_hba.conf file is installed when the data directory is initialized by initdb. The general format of the pg_hba.conf file is a set of records, one per line. Blank lines are ignored, as is any text after the # comment character. A record is made up of a number of fields which are separated by spaces and/or tabs. Fields can contain white space if the field value is quoted. Records cannot be continued across lines. Each record specifies a connection type, a client IP address range (if relevant for the connection type), a database name, a user name, and the authentication method to be used for connections matching these parameters. The first record with a matching connection type, client address, requested database, and user name is used to perform authentication. There is no "fall-through" or "backup": if one record is chosen and the authentication fails, subsequent records are not considered. If no record matches, access is denied. A record may have one of the seven formats local database user authentication-method [authentication-option] host database user CIDR-address authentication-method [authentication-option] host database user IP-address IP-mask authentication-method [authentication-option] hostssl database user IP-address IP-mask authentication-method [authentication-option] hostnossl database user IP-address IP-mask authentication-method [authentication-option] The meaning of the fields is as follows:
Since the pg_hba.conf records are examined sequentially for each connection attempt, the order of the records is significant. Typically, earlier records will have tight connection match parameters and weaker authentication methods, while later records will have looser match parameters and stronger authentication methods. For example, one might wish to use trust authentication for local TCP/IP connections but require a password for remote TCP/IP connections. In this case a record specifying trust authentication for connections from 127.0.0.1 would appear before a record specifying password authentication for a wider range of allowed client IP addresses.
The pg_hba.conf file is read on start-up and when the main server process receives a SIGHUP signal. If you edit the file on an active system, you will need to signal the server (using pg_ctl reload or kill -HUP) to make it re-read the file.
An example of a pg_hba.conf file is shown in Example 33-1. See the next section for details on the different authentication methods. Example 33-1. An example pg_hba.conf file # Allow any user on the local system to connect to any database under # any user name using Unix-domain sockets (the default for local # connections). # # TYPE DATABASE USER CIDR-ADDRESS METHOD local all all trust # The same using local loopback TCP/IP connections. # # TYPE DATABASE USER CIDR-ADDRESS METHOD host all all 127.0.0.1/32 trust # The same as the last line but using a separate netmask column # # TYPE DATABASE USER CIDR-ADDRESS METHOD host all all 127.0.0.1 255.255.255.255 trust # Allow any user from any host with IP address 192.168.93.x to connect # to database "template1" as the same user name that ident reports for # the connection (typically the Unix user name). # # TYPE DATABASE USER CIDR-ADDRESS METHOD host template1 all 192.168.93.0/24 ident sameuser # The same as the last line but using a separate netmask column # # TYPE DATABASE USER CIDR-ADDRESS METHOD host template1 all 192.168.93.0 255.255.255.0 ident sameuser # Allow a user from host 192.168.12.10 to connect to database # "template1" if the user's password is correctly supplied. # # TYPE DATABASE USER CIDR-ADDRESS METHOD host template1 all 192.168.12.10/32 md5 # In the absence of preceding "host" lines, these two lines will # reject all connection from 192.168.54.1 (since that entry will be # matched first), but allow Kerberos V connections from anywhere else # on the Internet. The zero mask means that no bits of the host IP # address are considered so it matches any host. # # TYPE DATABASE USER CIDR-ADDRESS METHOD host all all 192.168.54.1/32 reject host all all 0.0.0.0/0 krb5 # Allow users from 192.168.x.x hosts to connect to any database, if # they pass the ident check. If, for example, ident says the user is # "bryanh" and he requests to connect as EnterpriseDB user "guest1", the # connection is allowed if there is an entry in pg_ident.conf for map # "omicron" that says "bryanh" is allowed to connect as "guest1". # # TYPE DATABASE USER CIDR-ADDRESS METHOD host all all 192.168.0.0/16 ident omicron # If these are the only three lines for local connections, they will # allow local users to connect only to their own databases (databases # with the same name as their user name) except for administrators and # members of group "support" who may connect to all databases. The file # $PGDATA/admins contains a list of user names. Passwords are required in # all cases. # # TYPE DATABASE USER CIDR-ADDRESS METHOD local sameuser all md5 local all @admins md5 local all +support md5 # The last two lines above can be combined into a single line: local all @admins,+support md5 # The database column can also use lists and file names, but not groups: local db1,db2,@demodbs all md5 |