The catalog pg_authid contains information about database authorization identifiers (roles). A role subsumes the concepts of "users" and "groups". A user is essentially just a role with the rolcanlogin flag set. Any role (with or without rolcanlogin) can have other roles as members; see pg_auth_members.
Since this catalog contains passwords, it must not be publicly readable. pg_roles is a publicly readable view on pg_authid that blanks out the password field.
Chapter 20 contains detailed information about user and privilege management.
Because user identities are cluster-wide, pg_authid is shared across all databases of a cluster: there is only one copy of pg_authid per cluster, not one per database.
Table 45-8. pg_authid Columns
|rolsuper||bool||Role has superuser privileges|
|rolinherit||bool||Role automatically inherits privileges of roles it is a member of|
|rolcreaterole||bool||Role can create more roles|
|rolcreatedb||bool||Role can create databases|
|rolcatupdate||bool||Role can update system catalogs directly. (Even a superuser cannot do this unless this column is true)|
|rolcanlogin||bool||Role can log in. That is, this role can be given as the initial session authorization identifier|
|rolconnlimit||int4||For roles that can log in, this sets maximum number of concurrent connections this role can make. -1 means no limit.|
|rolpassword||text||Password (possibly encrypted); null if none. If the password is encrypted, this column will contain the string md5 followed by a 32-character hexadecimal MD5 hash. The MD5 hash will be of the user's password concatenated to their username (for example, if user joe has password xyzzy, PostgreSQL will store the md5 hash of xyzzyjoe).|
|rolvaliduntil||timestamptz||Password expiry time (only used for password authentication); null if no expiration|