chatwork-webhook-request-validation-on-aws-lambda.js

chatwork-webhook-request-validation-on-aws-lambda.js

exports.handler = function(event, context, callback) {        
    console.log('Received event:', JSON.stringify(event, null, 2));
    // Retrieve request parameters from the Lambda function input:
    var signature = event.headers['X-ChatWorkWebhookSignature'];
    var body = event.body;
 
    if (validate(signature, body)) {
        // write operation for webhook
        callback(null, {"statusCode": 200, "body": "Success"})
    }  else {
        // nop and return 403
        callback(null, {"statusCode": 403, "body": "Forbidden"})    }
}
 
var validate = function(signature, body){
    var cipheredBody = digest(body);
    return cipheredBody === signature;
}
 
var digest = function(value){
    var secret = decode(process.env.TOKEN);
    var crypto = require('crypto');
    var hash = crypto.createHmac('SHA256', secret).update(value).digest('base64');
    return hash;
}
 
var encode = function(value){
    var buffer = new Buffer(value);
    var encoded = buffer.toString('base64');
    return encoded;
}
 
var decode = function(value){
    var buffer = new Buffer(value, 'base64');
    return buffer;
}