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/**
 * Copyright (C) 2015 The Gravitee team (http://gravitee.io)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package io.gravitee.am.common.utils;

import java.security.SecureRandom;
import java.util.Base64;

/**
 * Random version-4 UUID will have 6 predetermined variant and version bits, leaving 122 bits for the randomly generated part.
 *
 * OAuth 2.0 spec says :
 *
 * The probability of an attacker guessing generated tokens (and other
 * credentials not intended for handling by end-users) MUST be less than
 * or equal to 2^(-128) and SHOULD be less than or equal to 2^(-160).
 *
 * This random generator use a 256-bit (32 byte) random value that is then URL-safe base64-encoded.
 *
 * @author Titouan COMPIEGNE (titouan.compiegne at graviteesource.com)
 * @author GraviteeSource Team
 */
public final class SecureRandomString {

    private static final SecureRandom random = new SecureRandom();
    private static final Base64.Encoder encoder = Base64.getUrlEncoder().withoutPadding();

    public static String generate() {
        byte[] buffer = new byte[32];
        random.nextBytes(buffer);
        return encoder.encodeToString(buffer);
    }
}