code: @Override
      public String extractSignedToken(String token) {
          String[] chunks = token.split("-", 3);
          if (chunks.length != 3) {
              // Invalid format
              return null;
          }
          String signature = chunks[0];
          String nonce = chunks[1];
          String raw = chunks[2];
          if (constantTimeEquals(signature, sign(nonce + "-" + raw))) {
              return raw;
          } else {
              return null;
          }
      }
docs: Extract a signed token that was signed by {@link #signToken(String)}.
  
  @param token The signed token to extract.
  @return The verified raw token, or null if the token isn't valid.