Bảo mật API tối ưu với Row Level Security trong Supabase

API Security with Row Level Security (RLS) in Supabase

Supabase is a powerful backend platform that combines PostgreSQL's robustness with modern tooling. One of its standout security features is Row Level Security (RLS), which lets you control exactly who can see and modify specific rows in your database tables. Understanding and implementing RLS properly is essential for building secure applications that handle sensitive data.

What is Row Level Security?

Row Level Security is a PostgreSQL feature that allows you to define policies determining which users can access which rows in a table. Instead of relying solely on application-level checks, RLS enforces these rules directly in the database. This means even if someone bypasses your application and connects directly to the database, they still can't access data they shouldn't see.

In Supabase, RLS is enabled by default on new tables, which is a security best practice. When enabled, every query must satisfy the defined policies, or it returns no results.

How RLS Works in Supabase

Supabase integrates RLS with its authentication system. When a user authenticates through Supabase Auth, they receive a token containing their user ID and any custom claims. This information becomes available in your database policies through special PostgreSQL functions.

The key concept is that policies are attached to tables and specify conditions that must be true for a query to return rows. These conditions can check the current user's ID, their role, or any other information available in the request context.

Setting Up Basic RLS Policies

Let's walk through a practical example. Imagine you're building a task management app where users have their own projects and tasks.

First, you need to enable RLS on your tables:

ALTER TABLE projects ENABLE ROW LEVEL SECURITY;
ALTER TABLE tasks ENABLE ROW LEVEL SECURITY;

Then create policies that allow users to access only their own data:

-- Allow users to view and create projects they own
CREATE POLICY "Users can view and create their own projects" ON projects
  FOR ALL
  USING (owner_id = auth.uid())
  WITH CHECK (owner_id = auth.uid());

-- Allow users to view tasks in their projects
CREATE POLICY "Users can view tasks in their projects" ON tasks
  FOR SELECT
  USING (project_id IN (SELECT id FROM projects WHERE owner_id = auth.uid()));

The auth.uid() function returns the ID of the currently authenticated user. The USING clause filters which rows are visible, while WITH CHECK controls which rows can be inserted or updated.

Handling Different User Roles

For more complex applications, you might need different access levels. Supabase Auth allows you to add custom claims to JWT tokens, which you can then use in your policies.

-- Check if user has admin role
CREATE POLICY "Admins can view all projects" ON projects
  FOR SELECT
  USING (auth.role() = 'admin' OR owner_id = auth.uid());

You can set custom claims when creating users through the Supabase API or Auth admin functions. These claims become available through the auth.role() function in your policies.

Securing API Endpoints

When building Supabase API endpoints, whether using Row Level Security or direct queries, always consider the principle of least privilege. Even with RLS enabled, your application code should only request the data it needs.

For example, instead of selecting all columns from a table, specify only what you need:

-- Good practice
SELECT id, name, status FROM tasks WHERE project_id = $1;

-- Avoid unless necessary
SELECT * FROM tasks WHERE project_id = $1;

This approach reduces the risk of accidentally exposing sensitive data and can improve performance.

Common RLS Patterns

Several patterns emerge when working with RLS in real applications:

Multi-tenant applications: Filter data by tenant ID or organization ID using the authenticated user's membership information. Content moderation: Allow certain users to access and moderate content while regular users can only see approved items. Audit trails: Track who created or modified each row by automatically setting user ID columns using database triggers. Soft deletes: Instead of physically deleting rows, mark them as deleted and filter them out in your RLS policies.

Testing Your Policies

Before deploying to production, thoroughly test your RLS policies. Supabase provides tools for this:

- Use the SQL Editor to run queries as different users - Test edge cases where users should be denied access - Verify that new users can access only what they should

You can simulate different users by setting the Authorization header with their JWT token when making API calls.

Performance Considerations

RLS policies can impact query performance, especially on large tables. Here are some optimization tips:

- Create indexes that support your policy conditions - Use IN clauses with subqueries judiciously - Consider partitioning large tables by user or tenant - Avoid complex functions in policy conditions when possible

Supabase provides query performance insights that can help you identify slow policies.

Advanced RLS Techniques

For sophisticated applications, you might need more advanced patterns:

Policy chaining: Use views with their own RLS policies to create layered security. Dynamic policies: Use application-specific metadata to determine access rights at query time. Time-based access: Implement policies that restrict access based on time windows or data freshness.

Security Best Practices

Beyond RLS itself, consider these security practices:

- Use HTTPS for all API calls - Implement rate limiting to prevent abuse - Regularly audit your policies and access patterns - Keep your Supabase project and dependencies updated - Use environment variables for sensitive configuration

Conclusion

Row Level Security in Supabase provides a robust foundation for building secure applications. By enforcing access controls at the database level, you create defense in depth that protects your data even if other layers are compromised.

The key to successful RLS implementation is thoughtful policy design that matches your application's access patterns while maintaining security. Start with simple policies, test thoroughly, and evolve them as your application grows.

Remember that security is an ongoing process, not a one-time setup. Regularly review your policies, monitor access patterns, and stay informed about new security features and best practices in the Supabase ecosystem.

By mastering RLS, you're not just protecting your data—you're building trust with your users and creating a foundation for scalable, secure applications that can grow with your needs.