Bearer tokens are essential for securing APIs and managing user sessions by granting access to protected resources without requiring continuous re-authentication. The two primary types of bearer tokens are JSON Web Tokens (JWTs) and opaque tokens, each with distinct features that influence their suitability for different applications. JWTs are self-contained, allowing for fast, stateless validation ideal for high-performance APIs and microservices, but they pose challenges in terms of revocation and potential data exposure if not properly encrypted. Opaque tokens, in contrast, are simple reference strings that necessitate server-side validation, offering better security and revocation control but at the cost of added overhead and reduced scalability. The decision between using JWTs or opaque tokens hinges on factors like the need for real-time revocation, data confidentiality, and the existing system architecture. Understanding these differences is crucial for ensuring application security, performance, and operational efficiency.