The MediaKeys interface of EncryptedMediaExtensions API the represents a set of keys that an associated HTMLMediaElement can use for decryption of media data during playback.
The MediaKeys.createSession() method returns a new MediaKeySession object, which represents a context for message exchange with a content decryption module (CDM).
The MediaKeys.setServerCertificate() method a Promise to a server certificate to be used to encrypt messages to the license server.