Which is a valid method to secure a REST API?

HTTPS with TLS encryption is the most common and effective method to secure REST APIs. TLS (Transport Layer Security) encrypts the communication channel between the client and the server, protecting data confidentiality and integrity, and authenticating the server. While XML encryption and XML signatures can secure the content of XML messages, they don't secure the transport layer itself, which is crucial for REST APIs that often use JSON. An MDS hash (MD5) is a cryptographic hash function primarily used for verifying data integrity, but it does not provide confidentiality or authentication. WS-Security is a set of extensions to SOAP for securing web services, not typically used for REST APIs.