SET SESSION AUTHORIZATION — set the session user identifier and the current user identifier of the current session
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION user_name
SET [ SESSION | LOCAL ] SESSION AUTHORIZATION DEFAULT
RESET SESSION AUTHORIZATION
   This command sets the session user identifier and the current user
   identifier of the current SQL session to be user_name.  The user name can be
   written as either an identifier or a string literal.  Using this
   command, it is possible, for example, to temporarily become an
   unprivileged user and later switch back to being a superuser.
  
   The session user identifier is initially set to be the (possibly
   authenticated) user name provided by the client.  The current user
   identifier is normally equal to the session user identifier, but
   might change temporarily in the context of SECURITY DEFINER
   functions and similar mechanisms; it can also be changed by
   SET ROLE.
   The current user identifier is relevant for permission checking.
  
The session user identifier can be changed only if the initial session user (the authenticated user) has the superuser privilege. Otherwise, the command is accepted only if it specifies the authenticated user name.
   The SESSION and LOCAL modifiers act the same
   as for the regular SET
   command.
  
   The DEFAULT and RESET forms reset the session
   and current user identifiers to be the originally authenticated user
   name.  These forms can be executed by any user.
  
   SET SESSION AUTHORIZATION cannot be used within a
   SECURITY DEFINER function.
  
SELECT SESSION_USER, CURRENT_USER; session_user | current_user --------------+-------------- peter | peter SET SESSION AUTHORIZATION 'paul'; SELECT SESSION_USER, CURRENT_USER; session_user | current_user --------------+-------------- paul | paul
   The SQL standard allows some other expressions to appear in place
   of the literal user_name, but these options
   are not important in practice.  PostgreSQL
   allows identifier syntax ("), which SQL
   does not.  SQL does not allow this command during a transaction;
   PostgreSQL does not make this
   restriction because there is no reason to.
   The username"SESSION and LOCAL modifiers are a
   PostgreSQL extension, as is the
   RESET syntax.
  
The privileges necessary to execute this command are left implementation-defined by the standard.