Validieren eines einfachen Token in der Anfrage

Die folgende Viewer-Anforderungsfunktion validiert ein JSON-Webtoken (JWT) in der Abfragezeichenfolge einer Anfrage. Wenn das Token gültig ist, gibt die Funktion die ursprüngliche, unveränderte Anfrage an zurück. CloudFront Wenn das Token nicht gültig ist, generiert die Funktion eine Fehlerantwort. Diese Funktion verwendet das crypto-Modul. Weitere Informationen finden Sie unter Integrierten Module.

Diese Funktion geht davon aus, dass Anforderungen einen JWT-Wert in einem Abfragezeichenfolgenparameter namens jwt enthalten.

Anmerkung

Um diese Funktion nutzen zu können, müssen Sie Ihre CloudFront KeyValueStore Amazon-ID in den Funktionscode eingeben.

Dieses Beispiel finden Sie unter GitHub.

JavaScript runtime 2.0

import crypto from 'crypto';
import cf from 'cloudfront';

//Response when JWT is not valid.
const response401 = {
    statusCode: 401,
    statusDescription: 'Unauthorized'
};

// Replace the KVS_ID with your KVS ID
const kvsId = "KVS_ID";
const kvsKey = 'jwt.secret';
// set to true to enable console logging
const loggingEnabled = false;


function jwt_decode(token, key, noVerify, algorithm) {
    // check token
    if (!token) {
        throw new Error('No token supplied');
    }
    // check segments
    const segments = token.split('.');
    if (segments.length !== 3) {
        throw new Error('Not enough or too many segments');
    }

    // All segment should be base64
    const headerSeg = segments[0];
    const payloadSeg = segments[1];
    const signatureSeg = segments[2];

    // base64 decode and parse JSON
    const payload = JSON.parse(_base64urlDecode(payloadSeg));

    if (!noVerify) {
        const signingMethod = 'sha256';
        const signingType = 'hmac';

        // Verify signature. `sign` will return base64 string.
        const signingInput = [headerSeg, payloadSeg].join('.');

        if (!_verify(signingInput, key, signingMethod, signingType, signatureSeg)) {
            throw new Error('Signature verification failed');
        }

        // Support for nbf and exp claims.
        // According to the RFC, they should be in seconds.
        if (payload.nbf && Date.now() < payload.nbf*1000) {
            throw new Error('Token not yet active');
        }

        if (payload.exp && Date.now() > payload.exp*1000) {
            throw new Error('Token expired');
        }
    }

    return payload;
}

//Function to ensure a constant time comparison to prevent
//timing side channels.
function _constantTimeEquals(a, b) {
    if (a.length != b.length) {
        return false;
    }
    
    let xor = 0;
    for (let i = 0; i < a.length; i++) {
    xor |= (a.charCodeAt(i) ^ b.charCodeAt(i));
    }
    
    return 0 === xor;
}

function _verify(input, key, method, type, signature) {
    if(type === "hmac") {
        return _constantTimeEquals(signature, _sign(input, key, method));
    }
    else {
        throw new Error('Algorithm type not recognized');
    }
}

function _sign(input, key, method) {
    return crypto.createHmac(method, key).update(input).digest('base64url');
}

function _base64urlDecode(str) {
    return Buffer.from(str, 'base64url')
}

async function handler(event) {
    let request = event.request;

    //Secret key used to verify JWT token.
    //Update with your own key.
    const secret_key = await getSecret()

    if(!secret_key) {
        return response401;
    }

    // If no JWT token, then generate HTTP redirect 401 response.
    if(!request.querystring.jwt) {
        log("Error: No JWT in the querystring");
        return response401;
    }

    const jwtToken = request.querystring.jwt.value;

    try{ 
        jwt_decode(jwtToken, secret_key);
    }
    catch(e) {
        log(e);
        return response401;
    }

    //Remove the JWT from the query string if valid and return.
    delete request.querystring.jwt;
    log("Valid JWT token");
    return request;
}

// get secret from key value store 
async function getSecret() {
    // initialize cloudfront kv store and get the key value 
    try {
        const kvsHandle = cf.kvs(kvsId);
        return await kvsHandle.get(kvsKey);
    } catch (err) {
        log(`Error reading value for key: ${kvsKey}, error: ${err}`);
        return null;
    }

}

function log(message) {
    if (loggingEnabled) {
        console.log(message);
    }
}

JavaScript runtime 1.0

var crypto = require('crypto');

//Response when JWT is not valid.
var response401 = {
    statusCode: 401,
    statusDescription: 'Unauthorized'
};

function jwt_decode(token, key, noVerify, algorithm) {
    // check token
    if (!token) {
        throw new Error('No token supplied');
    }
    // check segments
    var segments = token.split('.');
    if (segments.length !== 3) {
        throw new Error('Not enough or too many segments');
    }

    // All segment should be base64
    var headerSeg = segments[0];
    var payloadSeg = segments[1];
    var signatureSeg = segments[2];

    // base64 decode and parse JSON
    var header = JSON.parse(_base64urlDecode(headerSeg));
    var payload = JSON.parse(_base64urlDecode(payloadSeg));

    if (!noVerify) {
        var signingMethod = 'sha256';
        var signingType = 'hmac';

        // Verify signature. `sign` will return base64 string.
        var signingInput = [headerSeg, payloadSeg].join('.');

        if (!_verify(signingInput, key, signingMethod, signingType, signatureSeg)) {
            throw new Error('Signature verification failed');
        }

        // Support for nbf and exp claims.
        // According to the RFC, they should be in seconds.
        if (payload.nbf && Date.now() < payload.nbf*1000) {
            throw new Error('Token not yet active');
        }

        if (payload.exp && Date.now() > payload.exp*1000) {
            throw new Error('Token expired');
        }
    }

    return payload;
}

function _verify(input, key, method, type, signature) {
    if(type === "hmac") {
        return (signature === _sign(input, key, method));
    }
    else {
        throw new Error('Algorithm type not recognized');
    }
}

function _sign(input, key, method) {
    return crypto.createHmac(method, key).update(input).digest('base64url');
}

function _base64urlDecode(str) {
    return String.bytesFrom(str, 'base64url')
}

function handler(event) {
    var request = event.request;

    //Secret key used to verify JWT token.
    //Update with your own key.
    var key = "LzdWGpAToQ1DqYuzHxE6YOqi7G3X2yvNBot9mCXfx5k";

    // If no JWT token, then generate HTTP redirect 401 response.
    if(!request.querystring.jwt) {
        console.log("Error: No JWT in the querystring");
        return response401;
    }

    var jwtToken = request.querystring.jwt.value;

    try{ 
        jwt_decode(jwtToken, key);
    }
    catch(e) {
        console.log(e);
        return response401;
    }

    //Remove the JWT from the query string if valid and return.
    delete request.querystring.jwt;
    console.log("Valid JWT token");
    return request;
}