sentry/static/app/components/u2f/webAuthnHelper.tsx

// Copyright (c) 2019 GitHub, Inc.

// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.

// below is from https://github.com/github/webauthn-json/tree/66322fc5c12184c5269691ab5abaac79545a3916

export function base64urlToBuffer(baseurl64String: string): ArrayBuffer {
  // Base64url to Base64
  const padding = '=='.slice(0, (4 - (baseurl64String.length % 4)) % 4);
  const base64String = baseurl64String.replace(/-/g, '+').replace(/_/g, '/') + padding;

  // Base64 to binary string
  const str = atob(base64String);

  // Binary string to buffer
  const buffer = new ArrayBuffer(str.length);
  const byteView = new Uint8Array(buffer);
  for (let i = 0; i < str.length; i++) {
    byteView[i] = str.charCodeAt(i);
  }
  return buffer;
}

export function bufferToBase64url(buffer: ArrayBuffer): string {
  // Buffer to binary string
  const byteView = new Uint8Array(buffer);
  let str = '';
  for (const charCode of byteView) {
    str += String.fromCharCode(charCode);
  }

  // Binary string to base64
  const base64String = btoa(str);

  // Base64 to base64url
  // We assume that the base64url string is well-formed.
  const base64urlString = base64String
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=/g, '');
  return base64urlString;
}