Add session_role to postgresql modules (#43650)

* Allow session_role to be set for PostgreSQL

By implementing session_role it becomes possible to run the specific
PostgreSQL commands as a different role.
The usecase that is immediately served by this, is the one that one
ansible playbook can be shared by multiple users, which all have
their
own PostgreSQL login_user. They do not need to share login
credentials,
as they can share the role within the PostgreSQL database.

The following example may give some insight:

$ psql -U jdoe -X -d postgres

postgres=> CREATE DATABASE abc;
ERROR:  permission denied to create database
postgres=> set role postgres;
SET
postgres=# CREATE DATABASE abc;
CREATE DATABASE

fixes #43592

* Tests for session_role in PostgreSQL

* Bump version_added for session_role feature

* Remove explicit encrypted parameter from tests

lib/ansible/modules/database/postgresql/postgresql_db.py

@@ -41,6 +41,11 @@ options:
     description:
       - Character classification (LC_CTYPE) to use in the database (e.g. lower, upper, ...) Must match LC_CTYPE of template database unless C(template0)
         is used as template.
+  session_role:
+    version_added: "2.8"
+    description: |
+      Switch to session_role after connecting. The specified session_role must be a role that the current login_user is a member of.
+      Permissions checking for SQL commands is carried out as though the session_role were the one that had logged in originally.
   state:
     description: |
         The database state. present implies that the database should be created if necessary.
@@ -370,6 +375,7 @@ def main():
         target=dict(default="", type="path"),
         target_opts=dict(default=""),
         maintenance_db=dict(default="postgres"),
+        session_role=dict(),
     ))
 
     module = AnsibleModule(
@@ -391,6 +397,7 @@ def main():
     state = module.params["state"]
     changed = False
     maintenance_db = module.params['maintenance_db']
+    session_role = module.params["session_role"]
 
     # To use defaults values, keyword arguments must be absent, so
     # check which values are empty and don't include in the **kw
@@ -439,6 +446,12 @@ def main():
     except Exception as e:
         module.fail_json(msg="unable to connect to database: %s" % to_native(e), exception=traceback.format_exc())
 
+    if session_role:
+        try:
+            cursor.execute('SET ROLE %s' % pg_quote_identifier(session_role, 'role'))
+        except Exception as e:
+            module.fail_json(msg="Could not switch role: %s" % to_native(e), exception=traceback.format_exc())
+
     try:
         if module.check_mode:
             if state == "absent":