Dynamic Jwt Builder subtype coercion

[lhazlewood]

Probably for 1.0 to avoid breaking changes for 0.x:

Jwts.builder() can return a dynamic JwtBuilder that dynamically changes its return values based on the key specified, e.g.

Jwts.builder().secureWith(key) returns a ProtectedJwtBuilder
Jwts.builder().secureWith(PublicKey) returns a JweBuilder (because signatures cannot be created with public keys)
Jwts.builder().secureWith(PrivateKey) returns a JwsBuilder (because private keys cannot be used to encrypt for assymmetric key algorithms), etc.

from a previous local testing scratchpad:

SecretKey secretKey = TestKeys.getA128CBC_HS256();
        PublicKey pubKey = TestKeys.getRS256().getPair().getPublic();
        RSAPublicKey rsaPub = (RSAPublicKey)pubKey;
        PrivateKey privKey = TestKeys.getRS256().getPair().getPrivate();
        RSAPrivateKey rsaPriv = (RSAPrivateKey)privKey;

        ECPublicKey ecPub = (ECPublicKey)TestKeys.getES256().getPair().getPublic();
        ECPrivateKey ecPriv = (ECPrivateKey)TestKeys.getES256().getPair().getPrivate();

        //Jwts.builder().encryptWith(EncryptionAlgorithms.A128GCM).using(pubKey).producedBy(KeyAlgorithms.RSA_OAEP);
        //Jwts.builder().encryptWith(EncryptionAlgorithms.A128GCM).using(pubKey).and(KeyAlgorithms.RSA_OAEP);

        Jwts.builder().signWith(ecPriv, SignatureAlgorithms.ES256).compact();

        // .setKeyLocator(keyLocator)
        // .locateKeysWith(keyLocator)


//        Jwts.builder().secureWith(secretKey).using(SignatureAlgorithms.HS256).compact();
//        Jwts.builder().secureWith(Keys.forPassword("foo".toCharArray())).and(KeyAlgorithms.PBES2_HS256_A128KW).compact();
//        Jwts.builder().secureWith(secretKey).using(EncryptionAlgorithms.A128GCM).compact();
//        Jwts.builder().secureWith(privKey).using(SignatureAlgorithms.RS256);
//        Jwts.builder().secureWith(pubKey).and(KeyAlgorithms.ECDH_ES).using(EncryptionAlgorithms.A128GCM);
//        Jwts.builder().secureWith(rsaPub).and(KeyAlgorithms.ECDH_ES).using(EncryptionAlgorithms.A256GCM);

        //Jwts.builder().encryptWith(pubKey).using(EncryptionAlgorithms.A128GCM).withKeyFrom(KeyAlgorithms.RSA_OAEP);
        //Jwts.builder().encryptWith(pubKey).and(KeyAlgorithms.RSA_OAEP).using(EncryptionAlgorithms.A128GCM);
        //Jwts.builder().encryptWith(rsaPub, KeyAlgorithms.RSA_OAEP).compact();

        //Jwts.builder().encryptWith(pubKey, KeyAlgorithms.RSA_OAEP).using(EncryptionAlgorithms.A128GCM);


        //Jwts.builder().using(SignatureAlgorithms.RS256);

        Jwts.builder().signWith(privKey, SignatureAlgorithms.RS256).compact();

        Jwts.builder().encryptWith(EncryptionAlgorithms.A256GCM, secretKey).compact();

        Jwts.builder().encryptWith(EncryptionAlgorithms.A256GCM, ecPub, KeyAlgorithms.ECDH_ES);

        //Jwts.builder().encryptWith(EncryptionAlgorithms.A256GCM, pubKey, KeyAlgorithms.ECDH_ES).compact();

        //Jwts.builder().signWith(ecPub).using(SignatureAlgorithms.RS256).compact();

This issue represents the work to make such an API available for 1.0

[lhazlewood]

Deciding to close this after seeing the current master branch API after merging #279, 529f04d and 7ed0b77.

The overloaded methods signWith and encryptWith in the current master branch API (versus those proposed here) are short, simple, easily locatable and more simply documented. The coerced-multi-builder approach wouldn't really provide much (if any) additional benefits at the expense of complexity and potential confusion.