$ java --enable-preview -cp ... JwtSigning     (27.0.1.0.2+1)
== RS256 with an RSA key from PEM
header.payload = eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJhbmt1ciIsImlzcyI6Imh0dHBzOi8vYW5rdXJtLmNvbSJ9
signature bytes = 256, jwt parts = 3
ok: RS256 signature verifies with the public PEM
== ES256 with an EC key from PEM (the trap is the signature format)
SHA256withECDSA              -> DER, starts 0x30, length varies run to run, 70-72: true   (JWT readers reject this)
SHA256withECDSAinP1363Format -> R||S, length 64   (what RFC 7518 requires for ES256)
ok: ES256 signature is exactly 64 bytes
ok: ES256 signature verifies with the public PEM
== EdDSA with an Ed25519 key from PEM
EdDSA signature bytes = 64  (the PKCS#8 file holds no public key, so there is nothing to decode for verifying here)
exit=0