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) may 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 18 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 42-8. pg_authid Columns
|Role has superuser privileges
|Role automatically inherits privileges of roles it is a member of
|Role may create more roles
|Role may create databases
|Role may update system catalogs directly. (Even a superuser may not do this unless this column is true.)
|Role may log in, that is, this role can be given as the initial session authorization identifier.
|For roles that can log in, this sets maximum number of concurrent connections this role can make. -1 means no limit.
|Password (possibly encrypted); NULL if none
|Password expiry time (only used for password authentication); NULL if no expiration
|Session defaults for run-time configuration variables