@Override
                    protected MessageDigest initialValue() {
                        try {
                            return MessageDigest.getInstance("SHA-256");
                        } catch (NoSuchAlgorithmException e) {
                            throw new SdkClientException(
                                    "Unable to get SHA256 Function"
                                            + e.getMessage(), e);
                        }
                    }
Abstract base class for AWS signing protocol implementations. Provides
utilities commonly needed by signing protocols such as computing
canonicalized host names, query string parameters, etc.
<p>
Not intended to be sub-classed by developers.
aws-java-sdk-core/src/main/java/com/amazonaws/auth/AbstractAWSSigner.java