Combined JWT parsing

To parse tokens with any protection (plain, signed and encrypted) use the JWTParser class:

import com.nimbusds.jose.*;
import com.nimbusds.jwt.*;

JWT jwt;

try {
    jwt = JWTParser.parse(string);
} catch (ParseException e) {
    // Invalid JWT encoding
}

// Check the JWT type
if (jwt instanceof PlainJWT) {
    PlainJWT plainObject = (PlainJWT)jwt;
    // continue processing of plain JWT...
} else if (jwt instanceof SignedJWT) {
    SignedJWT jwsObject = (SignedJWT)jwt;
    // continue with signature verification...
} else if (jwt instanceof EncryptedJWT) {
    EncryptedJWT jweObject = (EncryptedJWT)jwt;
    // continue with decryption...
}

Use the JWTHandler interface or its JWTAdapter to handle parser output in more elegant and type-safe way, with support for generics:

import com.nimbusds.jose.*;
import com.nimbusds.jwt.*;

// Devise a type-self handler for the expected JWTs which returns the claims
// set after verification / decryption
class Handler implements JWTHandler<ReadOnlyJWTClaimsSet> {

    @Override
    public ReadOnlyJWTClaimsSet onPlainJWT(PlainJWT plainJWT) {
        return null; // Plain object claims not accepted
    }

    @Override
    public ReadOnlyJWTClaimsSet onSignedJWT(SignedJWT signedJWT) {
        // Verify signature
        boolean success = signedJWT.verify(...);
        if (success) {
            // Return claims
            return signedJWT.getClaimsSet();
        } else {
            return null;
        }
    }

    @Override
    public ReadOnlyJWTClaimsSet onEncryptedJWT(EncryptedJWT encryptedJWT) {
        // Decrypt
        encryptedJWT.decrypt(...);
        // Return claims after successful decryption
        return encryptedJWT.getClaimsSet();
    }
}

// Parse JWTs
ReadOnlyClaimsSet claims = JWTParser.parse(string, new Handler(...));