Custom node.js api's authorization with aws cognito permission rules - node.js

Question

I'm able to register and authenticate users via amazon-cognito-identity-js
and aws-sdk and the process to implement it was pretty much straightforward and simple. Now I have few APIs built in node.js, how would I authorize these APIs using Cognito policies (i.e permissions) and wrap them around logged in user where I'm already able to get idToken, accessToken and refreshToken.
Other things I came across while reading the documentation and watching video tutorials are aws-lambda and aws-api-gateway. I understood that aws-lambda is a way to define methods that can communicate with no-sql database (i.e AWS dynamo) and api-gateways to access those lambda functions and interact with DB and that all is serverless.
My question is, what if I have my own APIs written in Node.js and I need to integrate Cognito user pools with it and to protect those resources using AWS Cognito policies, user groups and roles, is it possible? Please guide me in this regard.

Answer 1

You can use the same authentication token which you get when you authorize the user to authorize your node.js APIs too. It can be done in many ways. One of the ways can be calling a isAuthenticated() method in each constructor which will check if there is a valid token or not.
export interface LoggedInCallBack{
isLoggedIn(message:string, loggedIn:boolean):void;
}
isAuthenticated(callBack : LoggedInCallBack){
if(callBack==null){
throw("User login service call cannot be null");
}
console.log("Is authneticated");
var cognitoUser = this.cognitoUtil.getCurrentUser();
console.log("Is cognito user empty? " + cognitoUser);
if(cognitoUser!=null){
cognitoUser.getSession(function (err, session){
if(err){
console.log("Couldn't get session:" + err);
callBack.isLoggedIn(err, false);
}
else{
console.log("Session is: " +session);
callBack.isLoggedIn(err, true);
}
})
}
else{
callBack.isLoggedIn("Cannot retrieve the current user", false);
}
}