CodeVerifier.ts

import * as crypto from 'crypto';

export class CodeVerifier {

    challenge: string;
    method: string;
    verifier: string;

    private base64URLEncode(value: Buffer) {
        return value.toString('base64')
            .replace(/\+/g, '-')
            .replace(/\//g, '_')
            .replace(/=/g, '');
    }

    public static sha256(value: string) {
        return crypto.createHash('sha256').update(value).digest();
    }

    private getVerifier() {
        return this.base64URLEncode(crypto.randomBytes(32));
    }


    constructor() {
        this.verifier = this.getVerifier();

        this.challenge = this.base64URLEncode(CodeVerifier.sha256(this.verifier));
        this.method = "S256";
    }
}