code: public boolean isMatch(String expectedSignature, Request request) {
          try {
              return isMatch(Base64.decode(expectedSignature), request);
          } catch (IOException e) {
              throw new RequestSigningException(e);
          }
      }
docs: Computes the signature for the provided request and determines whether
  it matches the expected signature (from the raw MessageBird-Signature header).
  
  @param expectedSignature Signature from the MessageBird-Signature
  header in its original base64 encoded state.
  @param request Request containing the values from the incoming webhook.
  @return True if the computed signature matches the expected signature.