byte[] getBytes() {
        if (request instanceof HttpEntityEnclosingRequestBase) {
            try {
                HttpEntity entity = ((HttpEntityEnclosingRequestBase) request).getEntity();
                return EntityUtils.toByteArray(entity);
            } catch (IOException e) {
                throw new UndeclaredThrowableException(e);
            }
        }
        return EMPTY_BYTES;
    }
Create canonical header set. The headers are ordered by name.

@param headers The set of headers to sign
@return The signing value from headers. Headers are separated with newline. Each header is
        formatted name:value with each header value whitespace trimmed and minimized
src/main/java/io/fabric8/maven/docker/access/ecr/AwsSigner4Request.java