Verifying JWT Signature using public key endpoint

Question

I\'m wanting to verify the signature of some JWTs from Microsoft. I\'m using Spring-Boot, the JJWT library and following endpoint: https://login.microsoftonline.com/common/d

Answer 1

x5c contains the certification chain. The first certificate of the chain must match with the key value represented by the other values in the JWK, in this case n and e, therefore the public key extracted from x5c[0] and the one built with n and e must be exactly the same

JWK values are encoded in base64url, not in base64. Change

BigInteger modulus = new BigInteger(1, Base64.decodeBase64(jsonKey.getN()));
BigInteger exponent = new BigInteger(1, Base64.decodeBase64(jsonKey.getE()));

with

BigInteger modulus = new BigInteger(1, Base64.getUrlDecoder().decode(jsonKey.getN()));
BigInteger exponent = new BigInteger(1, Base64.getUrlDecoder().decode(jsonKey.getE()));