Advanced PostgreSQL Role-Based Access Control: Row-Level Security and Policy Management

Introduction

PostgreSQL Row-Level Security (RLS) provides fine-grained access control at the row level, enabling you to enforce complex authorization rules directly in the database. This eliminates the need for application-layer filtering and ensures data security regardless of how applications access the database.

Why Row-Level Security?

Traditional Approach Problems

Application-layer filtering:

# Every query must remember to filter
query = "SELECT * FROM documents WHERE tenant_id = %s"
results = db.execute(query, [current_user_tenant_id])

Issues:
- Easy to forget filters (security vulnerabilities)
- Code duplication across application
- No protection for direct database access
- Complex audit requirements

Row-Level Security Benefits

• Automatic enforcement: Policies applied transparently
• Centralized rules: Security logic in one place
• Multi-tenant isolation: Perfect for SaaS applications
• Audit compliance: Built-in security guarantees
• Performance: Efficient query planning

Basic RLS Setup

Step 1: Enable RLS on Table

CREATE TABLE documents (
    id SERIAL PRIMARY KEY,
    title VARCHAR(200),
    content TEXT,
    owner_id INTEGER NOT NULL,
    department VARCHAR(50),
    is_public BOOLEAN DEFAULT false,
    created_at TIMESTAMP DEFAULT NOW()
);

-- Enable row-level security
ALTER TABLE documents ENABLE ROW LEVEL SECURITY;

Step 2: Create Roles

-- Create different user roles
CREATE ROLE regular_user;
CREATE ROLE department_manager;
CREATE ROLE admin;

-- Grant table access
GRANT SELECT, INSERT, UPDATE, DELETE ON documents TO regular_user;
GRANT SELECT, INSERT, UPDATE, DELETE ON documents TO department_manager;
GRANT ALL ON documents TO admin;

Step 3: Create Policies

-- Policy: Users can see their own documents
CREATE POLICY user_own_documents ON documents
    FOR SELECT
    TO regular_user
    USING (owner_id = current_setting('app.user_id')::INTEGER);

-- Policy: Users can insert documents owned by themselves
CREATE POLICY user_insert_own ON documents
    FOR INSERT
    TO regular_user
    WITH CHECK (owner_id = current_setting('app.user_id')::INTEGER);

-- Policy: Users can update their own documents
CREATE POLICY user_update_own ON documents
    FOR UPDATE
    TO regular_user
    USING (owner_id = current_setting('app.user_id')::INTEGER)
    WITH CHECK (owner_id = current_setting('app.user_id')::INTEGER);

Step 4: Set Session Variables

In application code:

import psycopg2

# Connect as role
conn = psycopg2.connect(
    host="localhost",
    database="mydb",
    user="regular_user",
    password="password"
)

# Set user context
cursor = conn.cursor()
cursor.execute("SET app.user_id = %s", [current_user_id])

# Now queries are automatically filtered
cursor.execute("SELECT * FROM documents")
# Only returns documents where owner_id = current_user_id

Multi-Tenant SaaS Application

Complete Multi-Tenant Setup

-- Create tenants table
CREATE TABLE tenants (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100) NOT NULL,
    created_at TIMESTAMP DEFAULT NOW()
);

-- Create users table
CREATE TABLE users (
    id SERIAL PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    tenant_id INTEGER REFERENCES tenants(id),
    role VARCHAR(20) NOT NULL,
    created_at TIMESTAMP DEFAULT NOW()
);

-- Create application data table
CREATE TABLE orders (
    id SERIAL PRIMARY KEY,
    tenant_id INTEGER NOT NULL REFERENCES tenants(id),
    customer_name VARCHAR(100),
    amount DECIMAL(10,2),
    status VARCHAR(20),
    created_by INTEGER REFERENCES users(id),
    created_at TIMESTAMP DEFAULT NOW()
);

-- Enable RLS
ALTER TABLE orders ENABLE ROW LEVEL SECURITY;

-- Policy: Users only see orders from their tenant
CREATE POLICY tenant_isolation ON orders
    FOR ALL
    TO public
    USING (tenant_id = current_setting('app.tenant_id')::INTEGER)
    WITH CHECK (tenant_id = current_setting('app.tenant_id')::INTEGER);

Application Integration

Django example:

from django.db import connection

class TenantMiddleware:
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        if request.user.is_authenticated:
            with connection.cursor() as cursor:
                cursor.execute(
                    "SET app.tenant_id = %s",
                    [request.user.tenant_id]
                )

        response = self.get_response(request)
        return response

Node.js example:

const { Pool } = require('pg');
const pool = new Pool();

async function setTenantContext(tenantId) {
    const client = await pool.connect();
    try {
        await client.query('SET app.tenant_id = $1', [tenantId]);
        return client;
    } catch (err) {
        client.release();
        throw err;
    }
}

// Usage
app.use(async (req, res, next) => {
    if (req.user) {
        req.dbClient = await setTenantContext(req.user.tenantId);
    }
    next();
});

Advanced Policy Patterns

1. Hierarchical Access Control

-- Users can see documents from their department and public ones
CREATE POLICY department_access ON documents
    FOR SELECT
    TO regular_user
    USING (
        department = current_setting('app.user_department', true)
        OR is_public = true
        OR owner_id = current_setting('app.user_id')::INTEGER
    );

2. Time-Based Access

CREATE TABLE subscriptions (
    id SERIAL PRIMARY KEY,
    user_id INTEGER NOT NULL,
    content TEXT,
    valid_from TIMESTAMP NOT NULL,
    valid_until TIMESTAMP NOT NULL
);

ALTER TABLE subscriptions ENABLE ROW LEVEL SECURITY;

-- Policy: Users can only see active subscriptions
CREATE POLICY active_subscriptions ON subscriptions
    FOR SELECT
    TO public
    USING (
        user_id = current_setting('app.user_id')::INTEGER
        AND NOW() BETWEEN valid_from AND valid_until
    );

3. Role-Based Access with Complex Logic

CREATE TABLE projects (
    id SERIAL PRIMARY KEY,
    name VARCHAR(100),
    owner_id INTEGER,
    team_id INTEGER,
    visibility VARCHAR(20) -- 'private', 'team', 'public'
);

ALTER TABLE projects ENABLE ROW LEVEL SECURITY;

-- Complex visibility policy
CREATE POLICY project_visibility ON projects
    FOR SELECT
    TO public
    USING (
        CASE current_setting('app.user_role', true)
            WHEN 'admin' THEN true
            WHEN 'manager' THEN (
                team_id = current_setting('app.user_team_id')::INTEGER
                OR visibility = 'public'
            )
            ELSE (
                owner_id = current_setting('app.user_id')::INTEGER
                OR visibility = 'public'
            )
        END
    );

4. Shared Access Lists

CREATE TABLE documents (
    id SERIAL PRIMARY KEY,
    title VARCHAR(200),
    owner_id INTEGER NOT NULL
);

CREATE TABLE document_shares (
    document_id INTEGER REFERENCES documents(id),
    shared_with_user_id INTEGER,
    permission VARCHAR(20), -- 'read', 'write'
    PRIMARY KEY (document_id, shared_with_user_id)
);

ALTER TABLE documents ENABLE ROW LEVEL SECURITY;

-- Policy: Users can see owned or shared documents
CREATE POLICY document_access ON documents
    FOR SELECT
    TO public
    USING (
        owner_id = current_setting('app.user_id')::INTEGER
        OR id IN (
            SELECT document_id 
            FROM document_shares 
            WHERE shared_with_user_id = current_setting('app.user_id')::INTEGER
        )
    );

-- Policy: Users can modify owned documents or those shared with write permission
CREATE POLICY document_modify ON documents
    FOR UPDATE
    TO public
    USING (
        owner_id = current_setting('app.user_id')::INTEGER
        OR id IN (
            SELECT document_id 
            FROM document_shares 
            WHERE shared_with_user_id = current_setting('app.user_id')::INTEGER
              AND permission = 'write'
        )
    );

Bypassing RLS for Administrative Tasks

Option 1: BYPASSRLS Role Attribute

-- Grant superuser-like access
CREATE ROLE admin_user WITH LOGIN PASSWORD 'secure_password';
ALTER ROLE admin_user BYPASSRLS;

-- Admin can see all rows regardless of policies

Option 2: Permissive Policies for Admins

-- Create permissive policy for admin role
CREATE POLICY admin_all_access ON documents
    FOR ALL
    TO admin
    USING (true)
    WITH CHECK (true);

Option 3: Disable RLS Temporarily

-- For maintenance scripts
BEGIN;
    ALTER TABLE documents DISABLE ROW LEVEL SECURITY;
    -- Perform administrative operations
    UPDATE documents SET archived = true WHERE created_at < NOW() - INTERVAL '1 year';
    ALTER TABLE documents ENABLE ROW LEVEL SECURITY;
COMMIT;

Policy Types: USING vs WITH CHECK

USING Clause

Controls which existing rows are visible/modifiable:

CREATE POLICY select_own ON documents
    FOR SELECT
    USING (owner_id = current_user_id());

-- User can only SELECT rows where owner_id matches

WITH CHECK Clause

Controls which new/updated rows are allowed:

CREATE POLICY insert_own ON documents
    FOR INSERT
    WITH CHECK (owner_id = current_user_id());

-- User can only INSERT rows where owner_id matches

Combined Policies

CREATE POLICY update_own ON documents
    FOR UPDATE
    USING (owner_id = current_user_id())       -- Can only update own rows
    WITH CHECK (owner_id = current_user_id()); -- Can't change ownership

Performance Considerations

1. Index Policy Columns

-- Create indexes for columns used in policies
CREATE INDEX idx_documents_owner ON documents(owner_id);
CREATE INDEX idx_documents_tenant ON documents(tenant_id);
CREATE INDEX idx_documents_department ON documents(department);

2. Analyze Query Plans

EXPLAIN ANALYZE
SELECT * FROM documents
WHERE title LIKE '%report%';

-- Check if policy filter is applied efficiently

3. Avoid Subqueries in Policies

Bad - Subquery executed for every row:

CREATE POLICY slow_policy ON documents
    USING (
        id IN (SELECT document_id FROM shares WHERE user_id = current_user_id())
    );

Better - Use EXISTS:

CREATE POLICY faster_policy ON documents
    USING (
        EXISTS (
            SELECT 1 FROM shares 
            WHERE document_id = documents.id 
              AND user_id = current_user_id()
        )
    );

Best - Use JOIN in application or materialized view:

CREATE MATERIALIZED VIEW user_accessible_documents AS
SELECT d.*, s.user_id AS shared_with
FROM documents d
LEFT JOIN shares s ON d.id = s.document_id;

CREATE INDEX ON user_accessible_documents(shared_with);

Monitoring and Auditing

View Active Policies

-- List all RLS policies
SELECT 
    schemaname,
    tablename,
    policyname,
    permissive,
    roles,
    cmd,
    qual,
    with_check
FROM pg_policies
ORDER BY tablename, policyname;

Audit Policy Changes

-- Create audit log for policy changes
CREATE TABLE policy_audit_log (
    id SERIAL PRIMARY KEY,
    table_name VARCHAR(100),
    policy_name VARCHAR(100),
    action VARCHAR(20),
    changed_by VARCHAR(50),
    changed_at TIMESTAMP DEFAULT NOW()
);

-- Trigger function to log changes
CREATE OR REPLACE FUNCTION log_policy_changes()
RETURNS event_trigger AS $$
BEGIN
    INSERT INTO policy_audit_log (table_name, policy_name, action, changed_by)
    SELECT 
        objid::regclass::text,
        object_identity,
        'CREATED',
        current_user
    FROM pg_event_trigger_ddl_commands()
    WHERE command_tag = 'CREATE POLICY';
END;
$$ LANGUAGE plpgsql;

CREATE EVENT TRIGGER log_policy_create
    ON ddl_command_end
    WHEN TAG IN ('CREATE POLICY')
    EXECUTE FUNCTION log_policy_changes();

Test Policy Effectiveness

-- Create test function
CREATE OR REPLACE FUNCTION test_user_access(
    test_user_id INTEGER,
    test_tenant_id INTEGER
)
RETURNS TABLE(document_id INTEGER, title VARCHAR) AS $$
BEGIN
    -- Set session variables
    PERFORM set_config('app.user_id', test_user_id::text, true);
    PERFORM set_config('app.tenant_id', test_tenant_id::text, true);

    -- Return accessible documents
    RETURN QUERY SELECT id, documents.title FROM documents;
END;
$$ LANGUAGE plpgsql SECURITY DEFINER;

-- Test access
SELECT * FROM test_user_access(123, 5);

Troubleshooting

Issue 1: Policies Not Applied

Check if RLS is enabled:

SELECT tablename, rowsecurity 
FROM pg_tables 
WHERE schemaname = 'public' AND tablename = 'documents';

Enable if disabled:

ALTER TABLE documents ENABLE ROW LEVEL SECURITY;

Issue 2: Session Variables Not Set

Debug current settings:

SHOW app.user_id;
SHOW app.tenant_id;

-- Or use current_setting
SELECT current_setting('app.user_id', true);

Issue 3: Performance Degradation

Identify slow policies:

EXPLAIN (ANALYZE, BUFFERS) 
SELECT * FROM documents WHERE title = 'test';

-- Look for "Filter" operations with policy conditions

Solution: Simplify policies or add indexes

Issue 4: Unexpected Access Denied

Test as specific user:

SET ROLE regular_user;
SET app.user_id = '123';

SELECT * FROM documents;
-- Shows what that user can actually see

RESET ROLE;

Best Practices

1. Always set session variables: Ensure current_setting() values are populated
2. Index policy columns: Create indexes on all columns used in USING/WITH CHECK
3. Test thoroughly: Verify policies with different roles and scenarios
4. Keep policies simple: Complex logic impacts performance
5. Use EXPLAIN: Analyze query plans with RLS enabled
6. Document policies: Comment policy logic for maintainability
7. Separate concerns: Use different policies for SELECT, INSERT, UPDATE, DELETE
8. Monitor performance: Set up alerts for slow queries

Conclusion

PostgreSQL Row-Level Security provides robust, database-enforced access control:

• Automatic filtering: Security applied transparently
• Multi-tenant isolation: Perfect for SaaS applications
• Flexible policies: Support complex authorization rules
• Centralized security: Logic in database, not scattered in code

Start with simple tenant isolation, test performance impacts, then expand to more sophisticated authorization patterns as needed.