pkceCoding.js

var array = new Uint8Array(32);
crypto.getRandomValues(array);
const verifier = base64urlencode(array);

const hexArray = SHA256(verifier).replace(/\r|\n/g, "").replace(/([\da-fA-F]{2}) ?/g, "0x$1 ").replace(/ +$/, "").split(" ");
const challenge = base64urlencode(hexArray);

return { verifier: verifier, challenge: challenge };

function base64urlencode(data){
    let string = String.fromCharCode.apply(null, data);
    return btoa(string).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
}

/**
*
*  btoa polyfill
*  https://github.com/davidchambers/Base64.js
*
*  Original code by David Chambers
*  See LICENSE for license details!
*
**/


function btoa(input){
    const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
    let output = '';

    for (let block = 0, charCode, i = 0, map = chars; 
        input.charAt(i | 0) || (map = '=', i % 1);  
        output += map.charAt(63 & block >> 8 - i % 1 * 8)) {
            charCode = input.charCodeAt(i += 3/4);

            if (charCode > 0xFF) {
                throw new Error("'btoa' failed: The string to be encoded contains characters outside of the Latin1 range.");
            }
            block = block << 8 | charCode;
    }
    return output;
}

/**
*
*  Secure Hash Algorithm (SHA256)
*  http://www.webtoolkit.info/
*
*  Original code by Angel Marin, Paul Johnston.
*  See buildApps/LICENSE for license details!
*
**/

function SHA256(string){
    var chrsz   = 8;
    var hexcase = 0;

    function safe_add (x, y) {
        var lsw = (x & 0xFFFF) + (y & 0xFFFF);
        var msw = (x >> 16) + (y >> 16) + (lsw >> 16);
        return (msw << 16) | (lsw & 0xFFFF);
    }

    function S (X, n) { return ( X >>> n ) | (X << (32 - n)); }
    function R (X, n) { return ( X >>> n ); }
    function Ch(x, y, z) { return ((x & y) ^ ((~x) & z)); }
    function Maj(x, y, z) { return ((x & y) ^ (x & z) ^ (y & z)); }
    function Sigma0256(x) { return (S(x, 2) ^ S(x, 13) ^ S(x, 22)); }
    function Sigma1256(x) { return (S(x, 6) ^ S(x, 11) ^ S(x, 25)); }
    function Gamma0256(x) { return (S(x, 7) ^ S(x, 18) ^ R(x, 3)); }
    function Gamma1256(x) { return (S(x, 17) ^ S(x, 19) ^ R(x, 10)); }
    
    function core_sha256 (m, l) {
        var K = new Array(0x428A2F98, 0x71374491, 0xB5C0FBCF, 0xE9B5DBA5, 0x3956C25B, 0x59F111F1, 0x923F82A4, 0xAB1C5ED5, 0xD807AA98, 0x12835B01, 0x243185BE, 0x550C7DC3, 0x72BE5D74, 0x80DEB1FE, 0x9BDC06A7, 0xC19BF174, 0xE49B69C1, 0xEFBE4786, 0xFC19DC6, 0x240CA1CC, 0x2DE92C6F, 0x4A7484AA, 0x5CB0A9DC, 0x76F988DA, 0x983E5152, 0xA831C66D, 0xB00327C8, 0xBF597FC7, 0xC6E00BF3, 0xD5A79147, 0x6CA6351, 0x14292967, 0x27B70A85, 0x2E1B2138, 0x4D2C6DFC, 0x53380D13, 0x650A7354, 0x766A0ABB, 0x81C2C92E, 0x92722C85, 0xA2BFE8A1, 0xA81A664B, 0xC24B8B70, 0xC76C51A3, 0xD192E819, 0xD6990624, 0xF40E3585, 0x106AA070, 0x19A4C116, 0x1E376C08, 0x2748774C, 0x34B0BCB5, 0x391C0CB3, 0x4ED8AA4A, 0x5B9CCA4F, 0x682E6FF3, 0x748F82EE, 0x78A5636F, 0x84C87814, 0x8CC70208, 0x90BEFFFA, 0xA4506CEB, 0xBEF9A3F7, 0xC67178F2);
        var HASH = new Array(0x6A09E667, 0xBB67AE85, 0x3C6EF372, 0xA54FF53A, 0x510E527F, 0x9B05688C, 0x1F83D9AB, 0x5BE0CD19);
        var W = new Array(64);

        var a, b, c, d, e, f, g, h, i, j;
        var T1, T2;
        m[l >> 5] |= 0x80 << (24 - l % 32);
        m[((l + 64 >> 9) << 4) + 15] = l;

        for ( var i = 0; i<m.length; i+=16 ) {

            a = HASH[0];
            b = HASH[1];
            c = HASH[2];
            d = HASH[3];
            e = HASH[4];
            f = HASH[5];
            g = HASH[6];
            h = HASH[7];

            for ( var j = 0; j<64; j++) {
                if (j < 16) W[j] = m[j + i];
                else W[j] = safe_add(safe_add(safe_add(Gamma1256(W[j - 2]), W[j - 7]), Gamma0256(W[j - 15])), W[j - 16]);
                T1 = safe_add(safe_add(safe_add(safe_add(h, Sigma1256(e)), Ch(e, f, g)), K[j]), W[j]);
                T2 = safe_add(Sigma0256(a), Maj(a, b, c));
                h = g;
                g = f;
                f = e;
                e = safe_add(d, T1);
                d = c;
                c = b;
                b = a;
                a = safe_add(T1, T2);
            }

            HASH[0] = safe_add(a, HASH[0]);
            HASH[1] = safe_add(b, HASH[1]);
            HASH[2] = safe_add(c, HASH[2]);
            HASH[3] = safe_add(d, HASH[3]);
            HASH[4] = safe_add(e, HASH[4]);
            HASH[5] = safe_add(f, HASH[5]);
            HASH[6] = safe_add(g, HASH[6]);
            HASH[7] = safe_add(h, HASH[7]);
        }

        return HASH;

    }

    function str2binb (str) {
        var bin = Array();
        var mask = (1 << chrsz) - 1;
        for(var i = 0; i < str.length * chrsz; i += chrsz) {
            bin[i>>5] |= (str.charCodeAt(i / chrsz) & mask) << (24 - i%32);
        }
        return bin;
    }

    function Utf8Encode(string) {
        string = string.replace(/\r\n/g,"\n");
        var utftext = "";
        for (var n = 0; n < string.length; n++) {
            var c = string.charCodeAt(n);
            if (c < 128) {
                utftext += String.fromCharCode(c);
            }else if((c > 127) && (c < 2048)) {
                utftext += String.fromCharCode((c >> 6) | 192);
                utftext += String.fromCharCode((c & 63) | 128);
            }else {
                utftext += String.fromCharCode((c >> 12) | 224);
                utftext += String.fromCharCode(((c >> 6) & 63) | 128);
                utftext += String.fromCharCode((c & 63) | 128);
            }
        }

        return utftext;

    }

    function binb2hex (binarray) {
        var hex_tab = hexcase ? "0123456789ABCDEF" : "0123456789abcdef";
        var str = "";
        for(var i = 0; i < binarray.length * 4; i++) {
            str += hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8+4)) & 0xF) +
            hex_tab.charAt((binarray[i>>2] >> ((3 - i%4)*8  )) & 0xF);
        }
        return str;
    }

    string = Utf8Encode(string);
    return binb2hex(core_sha256(str2binb(string), string.length * chrsz));
}