The JwkManager class, on source code lines 177-178 loads the RSA public key value "n" with: Base64.getDecoder()decode(n1).

This is not RFC (https://tools.ietf.org/html/rfc7517) compliant. The BigInts of the RSA key are Base64URL encoded. So that code should load "n" using Base64.getUrlDecoder().decode(n1).

(Note this also applies to the other key exponents such as "e" etc)

Also the creation of the BigInteger from n1/e1 is currently wrong as it is mandatory to use:

new BigInteger(1,b,0,b.length); //where b=byte[] = Base64.getUrlDecoder().decode(n1).

As per spec it is a Base64urlUInt (https://tools.ietf.org/html/rfc7518#section-6.3)!