To secure your GraphQL API, it's essential to address authentication and authorization first. Using JSON Web Tokens (JWTs) is a recommended approach for managing user auth. Additionally, limit query depth by using libraries like graphql-depth-limit, paginate list fields where appropriate, improve validation and sanitization, use timeouts to prevent slow or unresponsive services, rate limit APIs, analyze query cost, and implement safelist operations. To further enhance security, turn off introspection in production, mask errors, avoid schema autogeneration, and only allow Apollo Gateway to query subgraph services directly. By implementing these techniques, you can reduce the attack surface area of your GraphQL API and improve its overall security posture.