Client Authentication client authentication 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 for more information. Therefore, it is essential to restrict which database users can connect. As explained in , 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. The <filename>pg_hba.conf</filename> File pg_hba.conf Client authentication is controlled by a configuration file, which traditionally is named pg_hba.conf and is stored in the database cluster's data directory. (HBA stands for host-based authentication.) A default pg_hba.conf file is installed when the data directory is initialized by . It is possible to place the authentication configuration file elsewhere, however; see the configuration parameter. 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 can be continued onto the next line by ending the line with a backslash. (Backslashes are not special except at the end of a line.) 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 double-quoted. Quoting one of the keywords in a database, user, or address field (e.g., all or replication) makes the word lose its special meaning, and just match a database, user, or host with that name. Backslash line continuation applies even within quoted text or comments. Each authentication 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. Each record can be an include directive or an authentication record. Include directives specify files that can be included, that contain additional records. The records will be inserted in place of the include directives. Include directives only contain two fields: include, include_if_exists or include_dir directive and the file or directory to be included. The file or directory can be a relative or absolute path, and can be double-quoted. For the include_dir form, all files not starting with a . and ending with .conf will be included. Multiple files within an include directory are processed in file name order (according to C locale rules, i.e., numbers before letters, and uppercase letters before lowercase ones). A record can have several formats: local database user auth-method auth-options host database user address auth-method auth-options hostssl database user address auth-method auth-options hostnossl database user address auth-method auth-options hostgssenc database user address auth-method auth-options hostnogssenc database user address auth-method auth-options host database user IP-address IP-mask auth-method auth-options hostssl database user IP-address IP-mask auth-method auth-options hostnossl database user IP-address IP-mask auth-method auth-options hostgssenc database user IP-address IP-mask auth-method auth-options hostnogssenc database user IP-address IP-mask auth-method auth-options include file include_if_exists file include_dir directory The meaning of the fields is as follows: local This record matches connection attempts using Unix-domain sockets. Without a record of this type, Unix-domain socket connections are disallowed. host This record matches connection attempts made using TCP/IP. host records match SSL or non-SSL connection attempts as well as GSSAPI encrypted or non-GSSAPI encrypted connection attempts. Remote TCP/IP connections will not be possible unless the server is started with an appropriate value for the configuration parameter, since the default behavior is to listen for TCP/IP connections only on the local loopback address localhost. hostssl This record matches connection attempts made using TCP/IP, but only when the connection is made with SSL encryption. To make use of this option the server must be built with SSL support. Furthermore, SSL must be enabled by setting the configuration parameter (see for more information). Otherwise, the hostssl record is ignored except for logging a warning that it cannot match any connections. hostnossl This record type has the opposite behavior of hostssl; it only matches connection attempts made over TCP/IP that do not use SSL. hostgssenc This record matches connection attempts made using TCP/IP, but only when the connection is made with GSSAPI encryption. To make use of this option the server must be built with GSSAPI support. Otherwise, the hostgssenc record is ignored except for logging a warning that it cannot match any connections. hostnogssenc This record type has the opposite behavior of hostgssenc; it only matches connection attempts made over TCP/IP that do not use GSSAPI encryption. database Specifies which database name(s) this record matches. The value all specifies that it matches all databases. The value sameuser specifies that the record matches if the requested database has the same name as the requested user. The value samerole specifies that the requested user must be a member of the role with the same name as the requested database. (samegroup is an obsolete but still accepted spelling of samerole.) Superusers are not considered to be members of a role for the purposes of samerole unless they are explicitly members of the role, directly or indirectly, and not just by virtue of being a superuser. The value replication specifies that the record matches if a physical replication connection is requested, however, it doesn't match with logical replication connections. Note that physical replication connections do not specify any particular database whereas logical replication connections do specify it. Otherwise, this is the name of a specific PostgreSQL database or a regular expression. Multiple database names and/or regular expressions can be supplied by separating them with commas. If the database name starts with a slash (/), the remainder of the name is treated as a regular expression. (See for details of PostgreSQL's regular expression syntax.) A separate file containing database names and/or regular expressions can be specified by preceding the file name with @. user Specifies which database user name(s) this record matches. The value all specifies that it matches all users. Otherwise, this is either the name of a specific database user, a regular expression (when starting with a slash (/), or a group name preceded by +. (Recall that there is no real distinction between users and groups in PostgreSQL; a + mark really means match any of the roles that are directly or indirectly members of this role, while a name without a + mark matches only that specific role.) For this purpose, a superuser is only considered to be a member of a role if they are explicitly a member of the role, directly or indirectly, and not just by virtue of being a superuser. Multiple user names and/or regular expressions can be supplied by separating them with commas. If the user name starts with a slash (/), the remainder of the name is treated as a regular expression. (See for details of PostgreSQL's regular expression syntax.) A separate file containing user names and/or regular expressions can be specified by preceding the file name with @. address Specifies the client machine address(es) that this record matches. This field can contain either a host name, an IP address range, or one of the special key words mentioned below. An IP address range is specified using standard numeric notation for the range's starting address, then a slash (/) and a CIDR mask length. The mask length indicates the number of high-order bits of the client IP address that must match. Bits to the right of this should be zero in the given IP address. There must not be any white space between the IP address, the /, and the CIDR mask length. Typical examples of an IPv4 address range specified this way are 172.20.143.89/32 for a single host, or 172.20.143.0/24 for a small network, or 10.6.0.0/16 for a larger one. An IPv6 address range might look like ::1/128 for a single host (in this case the IPv6 loopback address) or fe80::7a31:c1ff:0000:0000/96 for a small network. 0.0.0.0/0 represents all IPv4 addresses, and ::0/0 represents all IPv6 addresses. To specify a single host, use a mask length of 32 for IPv4 or 128 for IPv6. In a network address, do not omit trailing zeroes. An entry given in IPv4 format will match only IPv4 connections, and an entry given in IPv6 format will match only IPv6 connections, even if the represented address is in the IPv4-in-IPv6 range. You can also write all to match any IP address, samehost to match any of the server's own IP addresses, or samenet to match any address in any subnet that the server is directly connected to. If a host name is specified (anything that is not an IP address range or a special key word is treated as a host name), that name is compared with the result of a reverse name resolution of the client's IP address (e.g., reverse DNS lookup, if DNS is used). Host name comparisons are case insensitive. If there is a match, then a forward name resolution (e.g., forward DNS lookup) is performed on the host name to check whether any of the addresses it resolves to are equal to the client's IP address. If both directions match, then the entry is considered to match. (The host name that is used in pg_hba.conf should be the one that address-to-name resolution of the client's IP address returns, otherwise the line won't be matched. Some host name databases allow associating an IP address with multiple host names, but the operating system will only return one host name when asked to resolve an IP address.) A host name specification that starts with a dot (.) matches a suffix of the actual host name. So .example.com would match foo.example.com (but not just example.com). When host names are specified in pg_hba.conf, you should make sure that name resolution is reasonably fast. It can be of advantage to set up a local name resolution cache such as nscd. Also, you may wish to enable the configuration parameter log_hostname to see the client's host name instead of the IP address in the log. These fields do not apply to local records. Users sometimes wonder why host names are handled in this seemingly complicated way, with two name resolutions including a reverse lookup of the client's IP address. This complicates use of the feature in case the client's reverse DNS entry is not set up or yields some undesirable host name. It is done primarily for efficiency: this way, a connection attempt requires at most two resolver lookups, one reverse and one forward. If there is a resolver problem with some address, it becomes only that client's problem. A hypothetical alternative implementation that only did forward lookups would have to resolve every host name mentioned in pg_hba.conf during every connection attempt. That could be quite slow if many names are listed. And if there is a resolver problem with one of the host names, it becomes everyone's problem. Also, a reverse lookup is necessary to implement the suffix matching feature, because the actual client host name needs to be known in order to match it against the pattern. Note that this behavior is consistent with other popular implementations of host name-based access control, such as the Apache HTTP Server and TCP Wrappers. IP-address IP-mask These two fields can be used as an alternative to the IP-address/mask-length notation. Instead of specifying the mask length, the actual mask is specified in a separate column. For example, 255.0.0.0 represents an IPv4 CIDR mask length of 8, and 255.255.255.255 represents a CIDR mask length of 32. These fields do not apply to local records. auth-method Specifies the authentication method to use when a connection matches this record. The possible choices are summarized here; details are in . All the options are lower case and treated case sensitively, so even acronyms like ldap must be specified as lower case. trust Allow the connection unconditionally. This method allows anyone that can connect to the PostgreSQL database server to login as any PostgreSQL user they wish, without the need for a password or any other authentication. See for details. reject Reject the connection unconditionally. This is useful for filtering out certain hosts from a group, for example a reject line could block a specific host from connecting, while a later line allows the remaining hosts in a specific network to connect. scram-sha-256 Perform SCRAM-SHA-256 authentication to verify the user's password. See for details. md5 Perform SCRAM-SHA-256 or MD5 authentication to verify the user's password. See for details. password Require the client to supply an unencrypted password for authentication. Since the password is sent in clear text over the network, this should not be used on untrusted networks. See for details. gss Use GSSAPI to authenticate the user. This is only available for TCP/IP connections. See for details. It can be used in conjunction with GSSAPI encryption. sspi Use SSPI to authenticate the user. This is only available on Windows. See for details. ident Obtain the operating system user name of the client by contacting the ident server on the client and check if it matches the requested database user name. Ident authentication can only be used on TCP/IP connections. When specified for local connections, peer authentication will be used instead. See for details. peer Obtain the client's operating system user name from the operating system and check if it matches the requested database user name. This is only available for local connections. See for details. ldap Authenticate using an LDAP server. See for details. radius Authenticate using a RADIUS server. See for details. cert Authenticate using SSL client certificates. See for details. pam Authenticate using the Pluggable Authentication Modules (PAM) service provided by the operating system. See for details. bsd Authenticate using the BSD Authentication service provided by the operating system. See for details. auth-options After the auth-method field, there can be field(s) of the form name=value that specify options for the authentication method. Details about which options are available for which authentication methods appear below. In addition to the method-specific options listed below, there is a method-independent authentication option clientcert, which can be specified in any hostssl record. This option can be set to verify-ca or verify-full. Both options require the client to present a valid (trusted) SSL certificate, while verify-full additionally enforces that the cn (Common Name) in the certificate matches the username or an applicable mapping. This behavior is similar to the cert authentication method (see ) but enables pairing the verification of client certificates with any authentication method that supports hostssl entries. On any record using client certificate authentication (i.e. one using the cert authentication method or one using the clientcert option), you can specify which part of the client certificate credentials to match using the clientname option. This option can have one of two values. If you specify clientname=CN, which is the default, the username is matched against the certificate's Common Name (CN). If instead you specify clientname=DN the username is matched against the entire Distinguished Name (DN) of the certificate. This option is probably best used in conjunction with a username map. The comparison is done with the DN in RFC 2253 format. To see the DN of a client certificate in this format, do openssl x509 -in myclient.crt -noout -subject -nameopt RFC2253 | sed "s/^subject=//" Care needs to be taken when using this option, especially when using regular expression matching against the DN. include This line will be replaced by the contents of the given file. include_if_exists This line will be replaced by the content of the given file if the file exists. Otherwise, a message is logged to indicate that the file has been skipped. include_dir This line will be replaced by the contents of all the files found in the directory, if they don't start with a . and end with .conf, processed in file name order (according to C locale rules, i.e., numbers before letters, and uppercase letters before lowercase ones). Files included by @ constructs are read as lists of names, which can be separated by either whitespace or commas. Comments are introduced by #, just as in pg_hba.conf, and nested @ constructs are allowed. Unless the file name following @ is an absolute path, it is taken to be relative to the directory containing the referencing file. 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 SIGHUPSIGHUP signal. If you edit the file on an active system, you will need to signal the postmaster (using pg_ctl reload, calling the SQL function pg_reload_conf(), or using kill -HUP) to make it re-read the file. The preceding statement is not true on Microsoft Windows: there, any changes in the pg_hba.conf file are immediately applied by subsequent new connections. The system view pg_hba_file_rules can be helpful for pre-testing changes to the pg_hba.conf file, or for diagnosing problems if loading of the file did not have the desired effects. Rows in the view with non-null error fields indicate problems in the corresponding lines of the file. To connect to a particular database, a user must not only pass the pg_hba.conf checks, but must have the CONNECT privilege for the database. If you wish to restrict which users can connect to which databases, it's usually easier to control this by granting/revoking CONNECT privilege than to put the rules in pg_hba.conf entries. Some examples of pg_hba.conf entries are shown in . See the next section for details on the different authentication methods. Example <filename>pg_hba.conf</filename> Entries # Allow any user on the local system to connect to any database with # any database user name using Unix-domain sockets (the default for local # connections). # # TYPE DATABASE USER ADDRESS METHOD local all all trust # The same using local loopback TCP/IP connections. # # TYPE DATABASE USER ADDRESS METHOD host all all 127.0.0.1/32 trust # The same as the previous line, but using a separate netmask column # # TYPE DATABASE USER IP-ADDRESS IP-MASK METHOD host all all 127.0.0.1 255.255.255.255 trust # The same over IPv6. # # TYPE DATABASE USER ADDRESS METHOD host all all ::1/128 trust # The same using a host name (would typically cover both IPv4 and IPv6). # # TYPE DATABASE USER ADDRESS METHOD host all all localhost trust # The same using a regular expression for DATABASE, that allows connection # to the database db1, db2 and any databases with a name beginning with "db" # and finishing with a number using two to four digits (like "db1234" or # "db12"). # # TYPE DATABASE USER ADDRESS METHOD local db1,"/^db\d{2,4}$",db2 all localhost trust # Allow any user from any host with IP address 192.168.93.x to connect # to database "postgres" as the same user name that ident reports for # the connection (typically the operating system user name). # # TYPE DATABASE USER ADDRESS METHOD host postgres all 192.168.93.0/24 ident # Allow any user from host 192.168.12.10 to connect to database # "postgres" if the user's password is correctly supplied. # # TYPE DATABASE USER ADDRESS METHOD host postgres all 192.168.12.10/32 scram-sha-256 # Allow any user from hosts in the example.com domain to connect to # any database if the user's password is correctly supplied. # # Require SCRAM authentication for most users, but make an exception # for user 'mike', who uses an older client that doesn't support SCRAM # authentication. # # TYPE DATABASE USER ADDRESS METHOD host all mike .example.com md5 host all all .example.com scram-sha-256 # In the absence of preceding "host" lines, these three lines will # reject all connections from 192.168.54.1 (since that entry will be # matched first), but allow GSSAPI-encrypted connections from anywhere else # on the Internet. The zero mask causes no bits of the host IP address to # be considered, so it matches any host. Unencrypted GSSAPI connections # (which "fall through" to the third line since "hostgssenc" only matches # encrypted GSSAPI connections) are allowed, but only from 192.168.12.10. # # TYPE DATABASE USER ADDRESS METHOD host all all 192.168.54.1/32 reject hostgssenc all all 0.0.0.0/0 gss host all all 192.168.12.10/32 gss # 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 PostgreSQL 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 ADDRESS METHOD host all all 192.168.0.0/16 ident map=omicron # If these are the only four lines for local connections, they will # allow local users to connect only to their own databases (databases # with the same name as their database user name) except for users whose # name end with "helpdesk", administrators and members of role "support", # who can connect to all databases. The file $PGDATA/admins contains a # list of names of administrators. Passwords are required in all cases. # # TYPE DATABASE USER ADDRESS METHOD local sameuser all md5 local all /^.*helpdesk$ 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: local db1,db2,@demodbs all md5 User Name Maps User name maps When using an external authentication system such as Ident or GSSAPI, the name of the operating system user that initiated the connection might not be the same as the database user (role) that is to be used. In this case, a user name map can be applied to map the operating system user name to a database user. To use user name mapping, specify map=map-name in the options field in pg_hba.conf. This option is supported for all authentication methods that receive external user names. Since different mappings might be needed for different connections, the name of the map to be used is specified in the map-name parameter in pg_hba.conf to indicate which map to use for each individual connection. User name maps are defined in the ident map file, which by default is named pg_ident.confpg_ident.conf and is stored in the cluster's data directory. (It is possible to place the map file elsewhere, however; see the configuration parameter.) The ident map file contains lines of the general forms: map-name system-username database-username include file include_if_exists file include_dir directory Comments, whitespace and line continuations are handled in the same way as in pg_hba.conf. The map-name is an arbitrary name that will be used to refer to this mapping in pg_hba.conf. The other two fields specify an operating system user name and a matching database user name. The same map-name can be used repeatedly to specify multiple user-mappings within a single map. As for pg_hba.conf, the lines in this file can be include directives, following the same rules. There is no restriction regarding how many database users a given operating system user can correspond to, nor vice versa. Thus, entries in a map should be thought of as meaning this operating system user is allowed to connect as this database user, rather than implying that they are equivalent. The connection will be allowed if there is any map entry that pairs the user name obtained from the external authentication system with the database user name that the user has requested to connect as. The value all can be used as the database-username to specify that if the system-user matches, then this user is allowed to log in as any of the existing database users. Quoting all makes the keyword lose its special meaning. If the database-username begins with a + character, then the operating system user can login as any user belonging to that role, similarly to how user names beginning with + are treated in pg_hba.conf. Thus, a + mark means match any of the roles that are directly or indirectly members of this role, while a name without a + mark matches only that specific role. Quoting a username starting with a + makes the + lose its special meaning. If the system-username field starts with a slash (/), the remainder of the field is treated as a regular expression. (See for details of PostgreSQL's regular expression syntax.) The regular expression can include a single capture, or parenthesized subexpression, which can then be referenced in the database-username field as \1 (backslash-one). This allows the mapping of multiple user names in a single line, which is particularly useful for simple syntax substitutions. For example, these entries mymap /^(.*)@mydomain\.com$ \1 mymap /^(.*)@otherdomain\.com$ guest will remove the domain part for users with system user names that end with @mydomain.com, and allow any user whose system name ends with @otherdomain.com to log in as guest. Quoting a database-username containing \1 does not make \1 lose its special meaning. If the database-username field starts with a slash (/), the remainder of the field is treated as a regular expression (see for details of PostgreSQL's regular expression syntax). It is not possible to use \1 to use a capture from regular expression on system-username for a regular expression on database-username. Keep in mind that by default, a regular expression can match just part of a string. It's usually wise to use ^ and $, as shown in the above example, to force the match to be to the entire system user name. The pg_ident.conf file is read on start-up and when the main server process receives a SIGHUPSIGHUP signal. If you edit the file on an active system, you will need to signal the postmaster (using pg_ctl reload, calling the SQL function pg_reload_conf(), or using kill -HUP) to make it re-read the file. The system view pg_ident_file_mappings can be helpful for pre-testing changes to the pg_ident.conf file, or for diagnosing problems if loading of the file did not have the desired effects. Rows in the view with non-null error fields indicate problems in the corresponding lines of the file. A pg_ident.conf file that could be used in conjunction with the pg_hba.conf file in is shown in . In this example, anyone logged in to a machine on the 192.168 network that does not have the operating system user name bryanh, ann, or robert would not be granted access. Unix user robert would only be allowed access when he tries to connect as PostgreSQL user bob, not as robert or anyone else. ann would only be allowed to connect as ann. User bryanh would be allowed to connect as either bryanh or as guest1. An Example <filename>pg_ident.conf</filename> File # MAPNAME SYSTEM-USERNAME PG-USERNAME omicron bryanh bryanh omicron ann ann # bob has user name robert on these machines omicron robert bob # bryanh can also connect as guest1 omicron bryanh guest1 Authentication Methods PostgreSQL provides various methods for authenticating users: Trust authentication, which simply trusts that users are who they say they are. Password authentication, which requires that users send a password. GSSAPI authentication, which relies on a GSSAPI-compatible security library. Typically this is used to access an authentication server such as a Kerberos or Microsoft Active Directory server. SSPI authentication, which uses a Windows-specific protocol similar to GSSAPI. Ident authentication, which relies on an Identification Protocol (RFC 1413) service on the client's machine. (On local Unix-socket connections, this is treated as peer authentication.) Peer authentication, which relies on operating system facilities to identify the process at the other end of a local connection. This is not supported for remote connections. LDAP authentication, which relies on an LDAP authentication server. RADIUS authentication, which relies on a RADIUS authentication server. Certificate authentication, which requires an SSL connection and authenticates users by checking the SSL certificate they send. PAM authentication, which relies on a PAM (Pluggable Authentication Modules) library. BSD authentication, which relies on the BSD Authentication framework (currently available only on OpenBSD). Peer authentication is usually recommendable for local connections, though trust authentication might be sufficient in some circumstances. Password authentication is the easiest choice for remote connections. All the other options require some kind of external security infrastructure (usually an authentication server or a certificate authority for issuing SSL certificates), or are platform-specific. The following sections describe each of these authentication methods in more detail. Trust Authentication When trust authentication is specified, PostgreSQL assumes that anyone who can connect to the server is authorized to access the database with whatever database user name they specify (even superuser names). Of course, restrictions made in the database and user columns still apply. This method should only be used when there is adequate operating-system-level protection on connections to the server. trust authentication is appropriate and very convenient for local connections on a single-user workstation. It is usually not appropriate by itself on a multiuser machine. However, you might be able to use trust even on a multiuser machine, if you restrict access to the server's Unix-domain socket file using file-system permissions. To do this, set the unix_socket_permissions (and possibly unix_socket_group) configuration parameters as described in . Or you could set the unix_socket_directories configuration parameter to place the socket file in a suitably restricted directory. Setting file-system permissions only helps for Unix-socket connections. Local TCP/IP connections are not restricted by file-system permissions. Therefore, if you want to use file-system permissions for local security, remove the host ... 127.0.0.1 ... line from pg_hba.conf, or change it to a non-trust authentication method. trust authentication is only suitable for TCP/IP connections if you trust every user on every machine that is allowed to connect to the server by the pg_hba.conf lines that specify trust. It is seldom reasonable to use trust for any TCP/IP connections other than those from localhost (127.0.0.1). Password Authentication MD5 SCRAM password authentication There are several password-based authentication methods. These methods operate similarly but differ in how the users' passwords are stored on the server and how the password provided by a client is sent across the connection. scram-sha-256 The method scram-sha-256 performs SCRAM-SHA-256 authentication, as described in RFC 7677. It is a challenge-response scheme that prevents password sniffing on untrusted connections and supports storing passwords on the server in a cryptographically hashed form that is thought to be secure. This is the most secure of the currently provided methods, but it is not supported by older client libraries. md5 The method md5 uses a custom less secure challenge-response mechanism. It prevents password sniffing and avoids storing passwords on the server in plain text but provides no protection if an attacker manages to steal the password hash from the server. Also, the MD5 hash algorithm is nowadays no longer considered secure against determined attacks. The md5 method cannot be used with the feature. To ease transition from the md5 method to the newer SCRAM method, if md5 is specified as a method in pg_hba.conf but the user's password on the server is encrypted for SCRAM (see below), then SCRAM-based authentication will automatically be chosen instead. password The method password sends the password in clear-text and is therefore vulnerable to password sniffing attacks. It should always be avoided if possible. If the connection is protected by SSL encryption then password can be used safely, though. (Though SSL certificate authentication might be a better choice if one is depending on using SSL). PostgreSQL database passwords are separate from operating system user passwords. The password for each database user is stored in the pg_authid system catalog. Passwords can be managed with the SQL commands and , e.g., CREATE ROLE foo WITH LOGIN PASSWORD 'secret', or the psql command \password. If no password has been set up for a user, the stored password is null and password authentication will always fail for that user. The availability of the different password-based authentication methods depends on how a user's password on the server is encrypted (or hashed, more accurately). This is controlled by the configuration parameter at the time the password is set. If a password was encrypted using the scram-sha-256 setting, then it can be used for the authentication methods scram-sha-256 and password (but password transmission will be in plain text in the latter case). The authentication method specification md5 will automatically switch to using the scram-sha-256 method in this case, as explained above, so it will also work. If a password was encrypted using the md5 setting, then it can be used only for the md5 and password authentication method specifications (again, with the password transmitted in plain text in the latter case). (Previous PostgreSQL releases supported storing the password on the server in plain text. This is no longer possible.) To check the currently stored password hashes, see the system catalog pg_authid. To upgrade an existing installation from md5 to scram-sha-256, after having ensured that all client libraries in use are new enough to support SCRAM, set password_encryption = 'scram-sha-256' in postgresql.conf, make all users set new passwords, and change the authentication method specifications in pg_hba.conf to scram-sha-256. GSSAPI Authentication GSSAPI GSSAPI is an industry-standard protocol for secure authentication defined in RFC 2743. PostgreSQL supports GSSAPI for authentication, communications encryption, or both. GSSAPI provides automatic authentication (single sign-on) for systems that support it. The authentication itself is secure. If GSSAPI encryption or SSL encryption is used, the data sent along the database connection will be encrypted; otherwise, it will not. GSSAPI support has to be enabled when PostgreSQL is built; see for more information. When GSSAPI uses Kerberos, it uses a standard service principal (authentication identity) name in the format servicename/hostname@realm. The principal name used by a particular installation is not encoded in the PostgreSQL server in any way; rather it is specified in the keytab file that the server reads to determine its identity. If multiple principals are listed in the keytab file, the server will accept any one of them. The server's realm name is the preferred realm specified in the Kerberos configuration file(s) accessible to the server. When connecting, the client must know the principal name of the server it intends to connect to. The servicename part of the principal is ordinarily postgres, but another value can be selected via libpq's connection parameter. The hostname part is the fully qualified host name that libpq is told to connect to. The realm name is the preferred realm specified in the Kerberos configuration file(s) accessible to the client. The client will also have a principal name for its own identity (and it must have a valid ticket for this principal). To use GSSAPI for authentication, the client principal must be associated with a PostgreSQL database user name. The pg_ident.conf configuration file can be used to map principals to user names; for example, pgusername@realm could be mapped to just pgusername. Alternatively, you can use the full username@realm principal as the role name in PostgreSQL without any mapping. PostgreSQL also supports mapping client principals to user names by just stripping 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. The location of the server's keytab file is specified by the configuration parameter. For security reasons, it is recommended to use a separate keytab just for the PostgreSQL server rather than allowing the server to read the system keytab file. Make sure that your server keytab file is readable (and preferably only readable, not writable) by the PostgreSQL server account. (See also .) The keytab file is generated using the Kerberos software; see the Kerberos documentation for details. The following example shows doing this using the kadmin tool of MIT Kerberos: kadmin% addprinc -randkey postgres/server.my.domain.org kadmin% ktadd -k krb5.keytab postgres/server.my.domain.org The following authentication options are supported for the GSSAPI authentication method: include_realm If set to 0, the realm name from the authenticated user principal is stripped off before being passed through the user name mapping (). This is discouraged and is primarily available for backwards compatibility, as it is not secure in multi-realm environments unless krb_realm is also used. It is recommended to leave include_realm set to the default (1) and to provide an explicit mapping in pg_ident.conf to convert principal names to PostgreSQL user names. map Allows mapping from client principals to database user names. See 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 is username@EXAMPLE.COM (or username/hostbased@EXAMPLE.COM, respectively), unless include_realm has been set to 0, in which case username (or username/hostbased) is what is seen as the system user name when mapping. krb_realm Sets 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. In addition to these settings, which can be different for different pg_hba.conf entries, there is the server-wide configuration parameter. If that is set to true, client principals are matched to user map entries case-insensitively. krb_realm, if set, is also matched case-insensitively. SSPI Authentication SSPI SSPI is a Windows technology for secure authentication with single sign-on. PostgreSQL will use SSPI in negotiate mode, which will use Kerberos when possible and automatically fall back to NTLM in other cases. SSPI and GSSAPI interoperate as clients and servers, e.g., an SSPI client can authenticate to an GSSAPI server. It is recommended to use SSPI on Windows clients and servers and GSSAPI on non-Windows platforms. When using Kerberos authentication, SSPI works the same way GSSAPI does; see for details. The following configuration options are supported for SSPI: include_realm If set to 0, the realm name from the authenticated user principal is stripped off before being passed through the user name mapping (). This is discouraged and is primarily available for backwards compatibility, as it is not secure in multi-realm environments unless krb_realm is also used. It is recommended to leave include_realm set to the default (1) and to provide an explicit mapping in pg_ident.conf to convert principal names to PostgreSQL user names. compat_realm If set to 1, the domain's SAM-compatible name (also known as the NetBIOS name) is used for the include_realm option. This is the default. If set to 0, the true realm name from the Kerberos user principal name is used. Do not disable this option unless your server runs under a domain account (this includes virtual service accounts on a domain member system) and all clients authenticating through SSPI are also using domain accounts, or authentication will fail. upn_username If this option is enabled along with compat_realm, the user name from the Kerberos UPN is used for authentication. If it is disabled (the default), the SAM-compatible user name is used. By default, these two names are identical for new user accounts. Note that libpq uses the SAM-compatible name if no explicit user name is specified. If you use libpq or a driver based on it, you should leave this option disabled or explicitly specify user name in the connection string. map Allows for mapping between system and database user names. See for details. For an SSPI/Kerberos principal, such as username@EXAMPLE.COM (or, less commonly, username/hostbased@EXAMPLE.COM), the user name used for mapping is username@EXAMPLE.COM (or username/hostbased@EXAMPLE.COM, respectively), unless include_realm has been set to 0, in which case username (or username/hostbased) is what is seen as the system user name when mapping. krb_realm Sets 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. Ident Authentication ident The ident authentication method works by obtaining the client's operating system user name from an ident server and using it as the allowed database user name (with an optional user name mapping). This is only supported on TCP/IP connections. When ident is specified for a local (non-TCP/IP) connection, peer authentication (see ) will be used instead. The following configuration options are supported for ident: map Allows for mapping between system and database user names. See for details. The Identification Protocol is described in RFC 1413. Virtually every Unix-like operating system ships with an ident server that listens on TCP port 113 by default. The basic functionality of an ident server is to answer questions like What user initiated the connection that goes out of your port X and connects to my port Y?. Since PostgreSQL knows both X and Y when a physical connection is established, it can interrogate the ident server on the host of the connecting client and can theoretically determine the operating system user for any given connection. The drawback of this procedure is that it depends on the integrity of the client: if the client machine is untrusted or compromised, an attacker could run just about any program on port 113 and return any user name they choose. This authentication method is therefore only appropriate for closed networks where each client machine is under tight control and where the database and system administrators operate in close contact. In other words, you must trust the machine running the ident server. Heed the warning:
RFC 1413 The Identification Protocol is not intended as an authorization or access control protocol.
Some ident servers have a nonstandard option that causes the returned user name to be encrypted, using a key that only the originating machine's administrator knows. This option must not be used when using the ident server with PostgreSQL, since PostgreSQL does not have any way to decrypt the returned string to determine the actual user name. Peer Authentication peer The peer authentication method works by obtaining the client's operating system user name from the kernel and using it as the allowed database user name (with optional user name mapping). This method is only supported on local connections. The following configuration options are supported for peer: map Allows for mapping between system and database user names. See for details. Peer authentication is only available on operating systems providing the getpeereid() function, the SO_PEERCRED socket parameter, or similar mechanisms. Currently that includes Linux, most flavors of BSD including macOS, and Solaris. LDAP Authentication LDAP This authentication method operates similarly to password except that it uses LDAP as the password verification method. LDAP is used only to validate the user name/password pairs. Therefore the user must already exist in the database before LDAP can be used for authentication. LDAP authentication can operate in two modes. In the first mode, which we will call the simple bind mode, the server will bind to the distinguished name constructed as prefix username suffix. Typically, the prefix parameter is used to specify cn=, or DOMAIN\ in an Active Directory environment. suffix is used to specify the remaining part of the DN in a non-Active Directory environment. In the second mode, which we will call the search+bind mode, the server first binds to the LDAP directory with a fixed user name and password, specified with ldapbinddn and ldapbindpasswd, and performs a search for the user trying to log in to the database. If no user and password is configured, an anonymous bind will be attempted to the directory. The search will be performed over the subtree at ldapbasedn, and will try to do an exact match of the attribute specified in ldapsearchattribute. Once the user has been found in this search, the server disconnects and re-binds to the directory as this user, using the password specified by the client, to verify that the login is correct. This mode is the same as that used by LDAP authentication schemes in other software, such as Apache mod_authnz_ldap and pam_ldap. This method allows for significantly more flexibility in where the user objects are located in the directory, but will cause two separate connections to the LDAP server to be made. The following configuration options are used in both modes: ldapserver Names or IP addresses of LDAP servers to connect to. Multiple servers may be specified, separated by spaces. ldapport Port number on LDAP server to connect to. If no port is specified, the LDAP library's default port setting will be used. ldapscheme Set to ldaps to use LDAPS. This is a non-standard way of using LDAP over SSL, supported by some LDAP server implementations. See also the ldaptls option for an alternative. ldaptls Set to 1 to make the connection between PostgreSQL and the LDAP server use TLS encryption. This uses the StartTLS operation per RFC 4513. See also the ldapscheme option for an alternative. Note that using ldapscheme or ldaptls only encrypts the traffic between the PostgreSQL server and the LDAP server. The connection between the PostgreSQL server and the PostgreSQL client will still be unencrypted unless SSL is used there as well. The following options are used in simple bind mode only: ldapprefix String to prepend to the user name when forming the DN to bind as, when doing simple bind authentication. ldapsuffix String to append to the user name when forming the DN to bind as, when doing simple bind authentication. The following options are used in search+bind mode only: ldapbasedn Root DN to begin the search for the user in, when doing search+bind authentication. ldapbinddn DN of user to bind to the directory with to perform the search when doing search+bind authentication. ldapbindpasswd Password for user to bind to the directory with to perform the search when doing search+bind authentication. ldapsearchattribute Attribute to match against the user name in the search when doing search+bind authentication. If no attribute is specified, the uid attribute will be used. ldapsearchfilter The search filter to use when doing search+bind authentication. Occurrences of $username will be replaced with the user name. This allows for more flexible search filters than ldapsearchattribute. ldapurl An RFC 4516 LDAP URL. This is an alternative way to write some of the other LDAP options in a more compact and standard form. The format is ldap[s]://host[:port]/basedn[?[attribute][?[scope][?[filter]]]] scope must be one of base, one, sub, typically the last. (The default is base, which is normally not useful in this application.) attribute can nominate a single attribute, in which case it is used as a value for ldapsearchattribute. If attribute is empty then filter can be used as a value for ldapsearchfilter. The URL scheme ldaps chooses the LDAPS method for making LDAP connections over SSL, equivalent to using ldapscheme=ldaps. To use encrypted LDAP connections using the StartTLS operation, use the normal URL scheme ldap and specify the ldaptls option in addition to ldapurl. For non-anonymous binds, ldapbinddn and ldapbindpasswd must be specified as separate options. LDAP URLs are currently only supported with OpenLDAP, not on Windows. It is an error to mix configuration options for simple bind with options for search+bind. When using search+bind mode, the search can be performed using a single attribute specified with ldapsearchattribute, or using a custom search filter specified with ldapsearchfilter. Specifying ldapsearchattribute=foo is equivalent to specifying ldapsearchfilter="(foo=$username)". If neither option is specified the default is ldapsearchattribute=uid. If PostgreSQL was compiled with OpenLDAP as the LDAP client library, the ldapserver setting may be omitted. In that case, a list of host names and ports is looked up via RFC 2782 DNS SRV records. The name _ldap._tcp.DOMAIN is looked up, where DOMAIN is extracted from ldapbasedn. Here is an example for a simple-bind LDAP configuration: host ... ldap ldapserver=ldap.example.net ldapprefix="cn=" ldapsuffix=", dc=example, dc=net" When a connection to the database server as database user someuser is requested, PostgreSQL will attempt to bind to the LDAP server using the DN cn=someuser, dc=example, dc=net and the password provided by the client. If that connection succeeds, the database access is granted. Here is an example for a search+bind configuration: host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchattribute=uid When a connection to the database server as database user someuser is requested, PostgreSQL will attempt to bind anonymously (since ldapbinddn was not specified) to the LDAP server, perform a search for (uid=someuser) under the specified base DN. If an entry is found, it will then attempt to bind using that found information and the password supplied by the client. If that second connection succeeds, the database access is granted. Here is the same search+bind configuration written as a URL: host ... ldap ldapurl="ldap://ldap.example.net/dc=example,dc=net?uid?sub" Some other software that supports authentication against LDAP uses the same URL format, so it will be easier to share the configuration. Here is an example for a search+bind configuration that uses ldapsearchfilter instead of ldapsearchattribute to allow authentication by user ID or email address: host ... ldap ldapserver=ldap.example.net ldapbasedn="dc=example, dc=net" ldapsearchfilter="(|(uid=$username)(mail=$username))" Here is an example for a search+bind configuration that uses DNS SRV discovery to find the host name(s) and port(s) for the LDAP service for the domain name example.net: host ... ldap ldapbasedn="dc=example,dc=net" Since LDAP often uses commas and spaces to separate the different parts of a DN, it is often necessary to use double-quoted parameter values when configuring LDAP options, as shown in the examples. RADIUS Authentication RADIUS This authentication method operates similarly to password except that it uses RADIUS as the password verification method. RADIUS is used only to validate the user name/password pairs. Therefore the user must already exist in the database before RADIUS can be used for authentication. When using RADIUS authentication, an Access Request message will be sent to the configured RADIUS server. This request will be of type Authenticate Only, and include parameters for user name, password (encrypted) and NAS Identifier. The request will be encrypted using a secret shared with the server. The RADIUS server will respond to this request with either Access Accept or Access Reject. There is no support for RADIUS accounting. Multiple RADIUS servers can be specified, in which case they will be tried sequentially. If a negative response is received from a server, the authentication will fail. If no response is received, the next server in the list will be tried. To specify multiple servers, separate the server names with commas and surround the list with double quotes. If multiple servers are specified, the other RADIUS options can also be given as comma-separated lists, to provide individual values for each server. They can also be specified as a single value, in which case that value will apply to all servers. The following configuration options are supported for RADIUS: radiusservers The DNS names or IP addresses of the RADIUS servers to connect to. This parameter is required. radiussecrets The shared secrets used when talking securely to the RADIUS servers. This must have exactly the same value on the PostgreSQL and RADIUS servers. It is recommended that this be a string of at least 16 characters. This parameter is required. The encryption vector used will only be cryptographically strong if PostgreSQL is built with support for OpenSSL. In other cases, the transmission to the RADIUS server should only be considered obfuscated, not secured, and external security measures should be applied if necessary. radiusports The port numbers to connect to on the RADIUS servers. If no port is specified, the default RADIUS port (1812) will be used. radiusidentifiers The strings to be used as NAS Identifier in the RADIUS requests. This parameter can be used, for example, to identify which database cluster the user is attempting to connect to, which can be useful for policy matching on the RADIUS server. If no identifier is specified, the default postgresql will be used. If it is necessary to have a comma or whitespace in a RADIUS parameter value, that can be done by putting double quotes around the value, but it is tedious because two layers of double-quoting are now required. An example of putting whitespace into RADIUS secret strings is: host ... radius radiusservers="server1,server2" radiussecrets="""secret one"",""secret two""" Certificate Authentication Certificate This authentication method uses SSL client certificates to perform authentication. It is therefore only available for SSL connections; see for SSL configuration instructions. When using this authentication method, the server will require that the client provide a valid, trusted certificate. No password prompt will be sent to the client. The cn (Common Name) attribute of the certificate will be compared to the requested database user name, and if they match the login will be allowed. User name mapping can be used to allow cn to be different from the database user name. The following configuration options are supported for SSL certificate authentication: map Allows for mapping between system and database user names. See for details. It is redundant to use the clientcert option with cert authentication because cert authentication is effectively trust authentication with clientcert=verify-full. PAM Authentication PAM This authentication method operates similarly to password except that it uses PAM (Pluggable Authentication Modules) as the authentication mechanism. The default PAM service name is postgresql. PAM is used only to validate user name/password pairs and optionally the connected remote host name or IP address. Therefore the user must already exist in the database before PAM can be used for authentication. For more information about PAM, please read the Linux-PAM Page. The following configuration options are supported for PAM: pamservice PAM service name. pam_use_hostname Determines whether the remote IP address or the host name is provided to PAM modules through the PAM_RHOST item. By default, the IP address is used. Set this option to 1 to use the resolved host name instead. Host name resolution can lead to login delays. (Most PAM configurations don't use this information, so it is only necessary to consider this setting if a PAM configuration was specifically created to make use of it.) If PAM is set up to read /etc/shadow, authentication will fail because the PostgreSQL server is started by a non-root user. However, this is not an issue when PAM is configured to use LDAP or other authentication methods. BSD Authentication BSD Authentication This authentication method operates similarly to password except that it uses BSD Authentication to verify the password. BSD Authentication is used only to validate user name/password pairs. Therefore the user's role must already exist in the database before BSD Authentication can be used for authentication. The BSD Authentication framework is currently only available on OpenBSD. BSD Authentication in PostgreSQL uses the auth-postgresql login type and authenticates with the postgresql login class if that's defined in login.conf. By default that login class does not exist, and PostgreSQL will use the default login class. To use BSD Authentication, the PostgreSQL user account (that is, the operating system user running the server) must first be added to the auth group. The auth group exists by default on OpenBSD systems. Authentication Problems Authentication failures and related problems generally manifest themselves through error messages like the following: FATAL: no pg_hba.conf entry for host "123.123.123.123", user "andym", database "testdb" This is what you are most likely to get if you succeed in contacting the server, but it does not want to talk to you. As the message suggests, the server refused the connection request because it found no matching entry in its pg_hba.conf configuration file. FATAL: password authentication failed for user "andym" Messages like this indicate that you contacted the server, and it is willing to talk to you, but not until you pass the authorization method specified in the pg_hba.conf file. Check the password you are providing, or check your Kerberos or ident software if the complaint mentions one of those authentication types. FATAL: user "andym" does not exist The indicated database user name was not found. FATAL: database "testdb" does not exist The database you are trying to connect to does not exist. Note that if you do not specify a database name, it defaults to the database user name. The server log might contain more information about an authentication failure than is reported to the client. If you are confused about the reason for a failure, check the server log.