pg-sync-roles 0.0.38

Python utility function to ensure that a PostgreSQL role has certain permissions or role memberships

pg-sync-roles

Python utility function to ensure that a PostgreSQL role has certain permissions or role memberships, and no others. While pg-sync-roles removes the need of a lot of the boilerplate in order to manage permissions, it is a light abstraction layer over the PostgreSQL permission system. Therefore to use pg-sync-roles effectively and securely, you should have knowledge of:

• PostgreSQL privileges
• PostgreSQL role attributes
• PostgreSQL database roles

pg-sync-roles should not be used on roles that should have permissions to multiple database in a cluster (although this limitation may be removed in future versions).

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Contents

• Features
• Installation
• Usage
• API
• Locking
• Under the hood
• Compatibility
• Running tests locally

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Features

• Transparently handles high numbers of permissions - avoiding "row is too big" errors.
• Locks where necessary - working around "tuple concurrently updated" or "tuple concurrently deleted" errors that can happen when permission changes are performed concurrently.
• Does not require the connecting user to be SUPERUSER
• Can grant (and so automatically revokes if not requested):
  • Login (with password and expiry)
  • Role memberships
  • Database CONNECT
  • Schema USAGE, CREATE, and ownership
  • Table (and table-like) SELECT
• Also automatically revokes all non-SELECT permissions on table-like objects, for example INSERT.
• Allows for contents of specific schemas to be ignored for the purposes of management of permissions

These features make pg-sync-roles useful when using PostgreSQL as a data warehouse with a high number of users that need granular permissions. The lack of SUPERUSER requirement means that pg-sync-roles is suitable for managed PostgreSQL clusters, for example in Amazon RDS.

Other types of privileges and other object types may be added in future versions.

Installation

pg-sync-roles can be installed from PyPI using pip. psycopg2 or psycopg (Psycopg 3) must also be explicitly installed.

pip install pg-sync-roles psycopg

Usage

To give a role the ability to login (with a random password valid for 28 days), CONNECT to a database, and membership of another role:

import string
import secrets
from datetime import datetime, timedelta, timezone
from pg_sync_roles import Login, DatabaseConnect, RoleMembership, sync_roles

# For example purposes, PostgreSQL can be run locally using this...
# docker run --rm -it -e POSTGRES_HOST_AUTH_METHOD=trust -p 5432:5432 postgres

# ... which should work with this engine
engine = sa.create_engine('postgresql+psycopg://postgres@127.0.0.1:5432/')

password_alphabet = string.ascii_letters + string.digits
password = ''.join(secrets.choice(password_alphabet) for i in range(64))

valid_until = datetime.now(timezone.utc) + timedelta(days=28)

with engine.connect() as conn:
    sync_roles(
        conn,
        'my_user_name',
        grants=(
            Login(password=password, valid_until=valid_until),
            DatabaseConnect('my_database_name'),
            RoleMembership('my_role_name'),
        ),
    )

Or to give a role SELECT on a table, USAGE on its schema, membersip of a role, and OWNERship+USAGE+CREATE of another schema:

from pg_sync_roles import (
    RoleMembership,
    SchemaUsage,
    SchemaCreate,
    SchemaOwnership,
    TableSelect,
    sync_roles,
)

engine = sa.create_engine('postgresql+psycopg://postgres@127.0.0.1:5432/')

with engine.connect() as conn:
    sync_roles(
        conn,
        'my_role_name',
        grants=(
            SchemaUsage('my_schema'),
            TableSelect('my_schema', 'my_table'),
            SchemaOwnership('my_other_schema'),
            SchemaUsage('my_other_schema'),
            SchemaCreate('my_other_schema'),
            RoleMembership('my_other_role'),
        ),
    )

API

Core function

sync_roles(conn, role_name, grants=(), preserve_existing_grants_in_schemas=(), lock_key=1)

• conn

  A SQLAlchemy connection with an engine of dialect postgresql+psycopg or postgresql+psycopg2. For SQLAlchemy < 2 future=True must be passed to its create_engine function.

• role_name

  The role name to grant and revoke permissions and role memberships from. If the role does not exist it will be automatically created.

• grants=()

  A tuple of grants of all permissions that the role specified by the role_name should have. Anything not in this list will be automatically revoked. See Grant types for the list of grant types.

• preserve_existing_grants_in_schemas=()

  A tuple of schema names. For each schema name sync_roles will leave any existing privileges granted on anything in the schema to role_name intact. This is useful in situations when the contents of the schemas are managed separately, outside of calls to sync_roles.

  A schema name being listed in preserve_existing_grants_in_schemas does not affect management of permissions on the the schema itself. In order for role_name to have privileges on these, they will have to be passed in via the grants parameter.

• lock_key=1

  The key for the advisory lock taken before changes are made. See Locking for more details.

Grant types

Login(password, valid_until)

DatabaseConnect(database_name)

SchemaUsage(schema_name)

SchemaCreate(schema_name)

TableSelect(schema_name, table_name)

RoleMembership(role_name)

SchemaOwnership(schema_name)

Locking

pg-sync-roles obtains an advisory exclusive lock before making any changes - this avoids "tuple concurrently updated" or "tuple concurrently deleted" errors that can be raised when multiple connections change or delete the same permissions-related rows. It does this by calling the pg_advisory_xact_lock(key bigint) function. By default a key of 1 is used, but this can be changed by passing a different integer key as the lock_key parameter to sync_roles.

If you have other processes changing permissions outide of the sync_roles function, they should first obtain the same lock by explicitly calling pg_advisory_xact_lock(key bigint) with the same key.

The advisory lock is only obtained if sync_roles detects there are changes to be made, and is released by the time it returns.

Under the hood

pg-sync-roles maintains a role per database perimission, a role per schema pemission, and a role per table permission. Rather than roles being granted permissions directly on objects, membership is granted to these roles that indirectly grant permissions on objects. This means that from the object's point of view, only 1 role has any given permission. This works around the de-facto limit on the number of roles that can have permission to any object.

The names of the roles maintained by pg-sync-roles begin with the prefix _pgsr_. Each name ends with a randomly generated unique identifier.

Compatibility

pg-sync-roles aims to be compatible with a wide range of Python and other dependencies:

• Python >= 3.7.1 (tested on 3.7.1, 3.8.0, 3.9.0, 3.10.0, and 3.11.0)
• psycopg2 >= 2.9.2 (tested on 3.9.2) and Psycopg 3 >= 3.1.4 (tested on 3.1.4)
• SQLAlchemy >= 1.4.24 (tested on 1.4.24 and 2.0.0)
• PostgreSQL >= 9.6 (tested on 9.6, 10.0, 11.0, 12.0, 13.0, 14.0, 15.0, and 16.0)

Note that SQLAlchemy < 2 does not support Psycopg 3, and for SQLAlchemy < 2 future=True must be passed to its create_engine function.

There are no plans to drop support for any of the above.

Running tests locally

python -m pip install psycopg -e ".[dev]"  # Only needed once
./start-services.sh                        # Only needed once
pytest