Java com.nimbusds.jose.jwk.JWKSet with custom field

I have a client sending in a JWKS like this:

{
  "keys": [
    "kty": "RSA",
    "use": "sig",
    "alg": "RS256",
    "kid": "...",
    "x5t": "...",
    "custom_field_1": "this is some content",
    "custom_field_2": "this is some content, too",
    "n": "...",
    "x5c": "..."
  ]
}

Using the com.nimbusds.jose.jwk.JWKSet, I'd like to rip through the keys via the getKeys() method, which gives me com.nimbusds.jose.jwk.JWK objects and read those custom fields. I need to perform some custom logic based on these fields.

Is there a way to do this?