code: public synchronized void updateKey(final byte[] key) {
          if (key == null || key.length == 0) {
              throw new IllegalArgumentException(SR.INVALID_KEY);
          }
  
          this.key = key;
          this.hmacSha256 = null;
      }
docs: Sets the name of the access key to be used when signing the request.
  
  @param key
  A <code>String</code> that represents the name of the access key to be used when signing the request.