@Override
  public String getEncryptionContext() {
    return context;
  }
Implementation of CloudBlobCryptoAgent, encrypts byte buffers by
1. generating a random encryption key
2. encrypting that random key with a key from KeyManagementService
   that is associated with the given context string
3. encrypting a data byte buffer with the generated random key
4. returning a byte buffer containing the serialized encrypted key
   and encrypted data (see {@link EncryptedDataPayload} below
   for serialization description
ambry-cloud/src/main/java/com/github/ambry/cloud/CloudBlobCryptoAgentImpl.java