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Java API for Telegram Bot API

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package com.pengrad.telegrambot.login;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.math.BigInteger;
import java.net.URI;
import java.security.InvalidKeyException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Date;
import java.util.Set;
import java.util.TreeSet;

/**
 * Stas Parshin
 * 18 June 2019
 */
public class CheckTelegramAuth {

    private final String botToken, dataCheck, hash;
    private final long authDate;

    public static CheckTelegramAuth fromUrl(String botToken, String authUrl) {
        return new CheckTelegramAuth(botToken, URI.create(authUrl).getQuery());
    }

    private CheckTelegramAuth(String botToken, String authQueryParams) {
        String hash = null;
        long authDate = 0;
        String[] params = authQueryParams.split("&");
        Set set = new TreeSet<>();
        for (String p : params) {
            if (p.startsWith("hash=")) {
                hash = p.substring(5);
            } else {
                set.add(p);
            }
            if (p.startsWith("auth_date=")) {
                authDate = Long.parseLong(p.substring(10));
            }
        }
        this.hash = hash;
        this.authDate = authDate;
        this.dataCheck = String.join("\n", set);
        this.botToken = botToken;
    }

    public Date authDate() {
        return new Date(authDate * 1000L);
    }

    public boolean isFromTelegram() throws Exception {
        byte[] secret = sha256(botToken.getBytes());
        String result = hmacSha256(secret, dataCheck);
        return result.equals(hash);
    }

    private static byte[] sha256(byte[] string) throws NoSuchAlgorithmException {
        MessageDigest md = MessageDigest.getInstance("SHA-256");
        return md.digest(string);
    }

    private static String hmacSha256(byte[] key, String data) throws NoSuchAlgorithmException, InvalidKeyException {
        Mac hmacSha256 = Mac.getInstance("HmacSHA256");
        SecretKeySpec secret_key = new SecretKeySpec(key, "HmacSHA256");
        hmacSha256.init(secret_key);
        byte[] result = hmacSha256.doFinal(data.getBytes());
        return hex(result);
    }

    private static String hex(byte[] str) {
        return String.format("%040x", new BigInteger(1, str));
    }

}