Method generateTOTPAtCounter

utils/totp.ts:34–56

* Generate TOTP at a specific counter value * @param secret Base32 encoded secret key * @param counter Time counter * @returns TOTP code

(
    secret: string,
    counter: number
  )

   * @returns TOTP code
   */
  private static generateTOTPAtCounter(
    secret: string,
    counter: number
  ): string {
    const decodedSecret = this.base32ToHex(secret)
    const timeHex = this.leftPad(counter.toString(16), 16)

    // Convert hex to WordArray for crypto-js
    const key = CryptoJS.enc.Hex.parse(decodedSecret)
    const message = CryptoJS.enc.Hex.parse(timeHex)

    // Calculate HMAC-SHA1
    const hmac = CryptoJS.HmacSHA1(message, key)
    const hmacResult = hmac.toString()

    const offset = parseInt(hmacResult.slice(-1), 16)
    const code = parseInt(hmacResult.substr(offset * 2, 8), 16) & 0x7fffffff

    return this.leftPad(
      (code % Math.pow(10, this.DIGITS)).toString(),
      this.DIGITS
    )
  }

  /**
   * Convert Base32 string to hexadecimal