What do you use for API security? How do you authorize the client and host-to-host?

For API security, it is important to ensure authentication, authorization, protection against attacks, and data encryption.

Client Authorization:

• Using OAuth 2.0 with access tokens (Bearer tokens).
• JWT (JSON Web Tokens) for transmitting user information and rights.
• API keys with restrictions on permissions and IP.

Host-to-host authorization:

• Using mTLS (Mutual TLS) — mutual authentication via certificates.
• IP filtering and VPNs to restrict access.
• Using HMAC signatures to verify the integrity and authenticity of requests.

Additionally:

• HTTPS for traffic encryption.
• Rate limiting.
• Logging and monitoring of suspicious activity.

Example of using mTLS for host-to-host:

1. The server and client have their own certificates.
2. During TLS connection establishment, both verify each other's certificates.
3. Only trusted hosts can establish a connection.

Thus, clients typically use tokens and keys, while host-to-host communication relies on certificates and secure channels.