SHA256算法

小程序项目需要引用腾讯的api，但是有个签名规则需要进行SHA256算法 对其加密，将生成的签名串（字节数组）使用 Base64 编码，即可获得最终的签名串，自己项目中就只用到了cryptoJS 中的AES加密，没有用到SHA256算法
所以就需要自己在去整一份加密方式

最简单前端使用SHA256

1.使用npm安装 ：npm install js-sha256
import { sha256 } from ‘js-sha256’ 或者 let sha256 = require(“js-sha256”).sha256//目录文件vue中引用
let newsha256 = sha256(“数据”)//要加密的数据

Base64 编码

浏览器上使用Base64 编码

window.atob()与window.btoa
Window.atob():函数用来解码一个已经被base-64编码过的数据
window.btoa()：将ascii字符串或二进制数据转换成一个base64编码过的字符串

小程序使用Base64 编码

因为不支持window对象所以得要自己写个js去进行编码转换
然后直接引用就是中的weBtoa 和weAtob 功能如浏览器上的一样

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var b64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
var b64re = /^(?:[A-Za-z\d+\/]{4})*?(?:[A-Za-z\d+\/]{2}(?:==)?|[A-Za-z\d+\/]{3}=?)?$/;
exports.weBtoa = function (string) {
    string = String(string);
    var bitmap, a, b, c, result = "", i = 0, rest = string.length % 3;
    for (; i < string.length;) {
        if ((a = string.charCodeAt(i++)) > 255 ||
            (b = string.charCodeAt(i++)) > 255 ||
            (c = string.charCodeAt(i++)) > 255)
            throw new TypeError("Failed to execute 'btoa' on 'Window': The string to be encoded contains characters outside of the Latin1 range.");
        bitmap = (a << 16) | (b << 8) | c;
        result += b64.charAt(bitmap >> 18 & 63) + b64.charAt(bitmap >> 12 & 63) +
            b64.charAt(bitmap >> 6 & 63) + b64.charAt(bitmap & 63);
    }
    return rest ? result.slice(0, rest - 3) + "===".substring(rest) : result;
};
exports.weAtob = function (string) {
    string = String(string).replace(/[\t\n\f\r ]+/g, "");
    if (!b64re.test(string))
        throw new TypeError("Failed to execute 'atob' on 'Window': The string to be decoded is not correctly encoded.");
    string += "==".slice(2 - (string.length & 3));
    var bitmap, result = "", r1, r2, i = 0;
    for (; i < string.length;) {
        bitmap = b64.indexOf(string.charAt(i++)) << 18 | b64.indexOf(string.charAt(i++)) << 12 |
            (r1 = b64.indexOf(string.charAt(i++))) << 6 | (r2 = b64.indexOf(string.charAt(i++)));
        result += r1 === 64 ? String.fromCharCode(bitmap >> 16 & 255) :
            r2 === 64 ? String.fromCharCode(bitmap >> 16 & 255, bitmap >> 8 & 255) :
                String.fromCharCode(bitmap >> 16 & 255, bitmap >> 8 & 255, bitmap & 255);
    }
    return result;
};
function b64DecodeUnicode(str) {
    return decodeURIComponent(exports.weAtob(str).replace(/(.)/g, function (p) {
        var code = p.charCodeAt(0).toString(16).toUpperCase();
        if (code.length < 2) {
            code = "0" + code;
        }
        return "%" + code;
    }));
}
function base64_url_decode(str) {
    var output = str.replace(/-/g, "+").replace(/_/g, "/");
    switch (output.length % 4) {
        case 0:
            break;
        case 2:
            output += "==";
            break;
        case 3:
            output += "=";
            break;
        default:
            throw "Illegal base64url string!";
    }
    try {
        return b64DecodeUnicode(output);
    }
    catch (err) {
        return exports.weAtob(output);
    }
}
function weappJwtDecode(token, options) {
    if (typeof token !== "string") {
        throw ("Invalid token specified");
    }
    options = options || {};
    var pos = options.header === true ? 0 : 1;
    try {
        return JSON.parse(base64_url_decode(token.split(".")[pos]));
    }
    catch (e) {
        throw ("Invalid token specified: " + e.message);
    }
}
exports.default = weappJwtDecode;