index.js

/*
  This code is "public domain". You can copy, modify, re-release and re-license,
  or incorporate into any other project without restriction of any kind.
  Tiny SHA256 by Geraint Luff - https://github.com/geraintluff/
*/

function sha256(r){function t(r,t){return r>>>t|r<<32-t}for(var h,n,o=Math.pow,e=o(2,32),f="",a=[],l=8*r.length,g=sha256.h=sha256.h||[],c=sha256.k=sha256.k||[],i=c.length,s={},u=2;i<64;u++)if(!s[u]){for(h=0;h<313;h+=u)s[h]=u;g[i]=o(u,.5)*e|0,c[i++]=o(u,1/3)*e|0}for(r+="€";r.length%64-56;)r+="\0";for(h=0;h<r.length;h++){if((n=r.charCodeAt(h))>>8)return;a[h>>2]|=n<<(3-h)%4*8}for(a[a.length]=l/e|0,a[a.length]=l,n=0;n<a.length;){var v=a.slice(n,n+=16),k=g;for(g=g.slice(0,8),h=0;h<64;h++){var d=v[h-15],p=v[h-2],w=g[0],A=g[4],C=g[7]+(t(A,6)^t(A,11)^t(A,25))+(A&g[5]^~A&g[6])+c[h]+(v[h]=h<16?v[h]:v[h-16]+(t(d,7)^t(d,18)^d>>>3)+v[h-7]+(t(p,17)^t(p,19)^p>>>10)|0);(g=[C+((t(w,2)^t(w,13)^t(w,22))+(w&g[1]^w&g[2]^g[1]&g[2]))|0].concat(g))[4]=g[4]+C|0}for(h=0;h<8;h++)g[h]=g[h]+k[h]|0}for(h=0;h<8;h++)for(n=3;n+1;n--){var M=g[h]>>8*n&255;f+=(M<16?0:"")+M.toString(16)}return f}

function getRandomBytes(length) {
  const bytes = new Uint8Array(length)
  window.crypto.getRandomValues(bytes)
  return bytes
}

function arrayBufferToBase64(buffer) {
  const bytes = new Uint8Array(buffer);
    const binary = bytes.reduce((previousValue, currentValue) => {
    return previousValue + String.fromCharCode(currentValue)
  }, "")
  return btoa(binary);
}

function base64URLEncode(str) {
  return arrayBufferToBase64(str)
      .replace(/\+/g, '-')
      .replace(/\//g, '_')
      .replace(/=/g, '')
}

function hexStringToBytes(str) {
  return Array.from(str.match(/.{1,2}/g), byte => {
    return parseInt(byte, 16)
  })
}

/**
 * Generates a Proof Key for Code Exchange (PKCE) challenge pair.
 * @see https://datatracker.ietf.org/doc/html/rfc7636
 */
function pkce() {
  if (typeof window !== "object") {
      throw new Error("This code is only meant to run in a browser environment.");
  }

  const verifier  = base64URLEncode(getRandomBytes(32))
  const challenge = base64URLEncode(hexStringToBytes(sha256(verifier)))
  return {"code_verifier": verifier, "code_challenge": challenge}
}

module.exports = pkce