Local JWT decoder.

gistfile1.txt

package com.govisdom.flow.services.auth;

import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.Map;
import java.util.stream.Collectors;

import com.auth0.jwt.exceptions.JWTDecodeException;
import com.auth0.jwt.impl.JWTParser;

import doublefin.auth.dto.JwtToken;

public class LocalJwtDecoder {

    public static JwtToken decode(String jwt) {
        JWTParser converter = new JWTParser();
        final var parts = splitToken(jwt);
        String headerJson;
        String payloadJson;
        try {
            headerJson = new String(Base64.getUrlDecoder().decode(parts[0]), StandardCharsets.UTF_8);
            payloadJson = new String(Base64.getUrlDecoder().decode(parts[1]), StandardCharsets.UTF_8);
        } catch (NullPointerException e) {
            throw new JWTDecodeException("The UTF-8 Charset isn't initialized.", e);
        } catch (IllegalArgumentException e) {
            throw new JWTDecodeException("The input is not a valid base 64 encoded string.", e);
        }
        final var header = converter.parseHeader(headerJson);
        final var payload = converter.parsePayload(payloadJson);

        final var claims = payload.getClaims().entrySet().stream()
            .collect(Collectors.toMap(Map.Entry::getKey, (e) -> e.getKey().equals("exp") ? Long.toString(e.getValue().asLong()) : e.getValue().asString()));

        return new JwtToken("API", payload.getExpiresAt(), payload.getSubject(), claims);
    }

    private static String[] splitToken(String token) throws JWTDecodeException {
        String[] parts = token.split("\\.");
        if (parts.length == 2 && token.endsWith(".")) {
            //Tokens with alg='none' have empty String as Signature.
            parts = new String[]{parts[0], parts[1], ""};
        }
        if (parts.length != 3) {
            throw new JWTDecodeException(
                String.format("The token was expected to have 3 parts, but got %s.", parts.length));
        }
        return parts;
    }
}