# Chapter 21. Client Authentication

Table of Contents

21.1. The pg_hba.conf File

21.2. User Name Maps

21.3. Authentication Methods

21.4. Trust Authentication

21.5. Password Authentication

21.6. GSSAPI Authentication

21.7. SSPI Authentication

21.8. Ident Authentication

21.9. Peer Authentication

21.10. LDAP Authentication

21.11. RADIUS Authentication

21.12. Certificate Authentication

21.13. PAM Authentication

21.14. BSD Authentication

21.15. Authentication Problems

When a client application connects to the database server, it specifies which PostgreSQL database 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 22 for more information. Therefore, it is essential to restrict which database users can connect.

# Note

As explained in Chapter 22, PostgreSQL actually does privilege management in terms of “roles”. In this chapter, we consistently use database user to mean “role with the LOGIN privilege”.

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 database user name that was requested.

PostgreSQL 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.

PostgreSQL database 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 might 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.