AWS - How to get username from token in a NodeJs Lamda? - node.js

Question

I use a NodeJs Lambda after an API Gateway.
var AWS = require('aws-sdk');
const cognito = new AWS.CognitoIdentityServiceProvider({apiVersion: '2016-04-18'})
exports.handler = async (event) => {
const token = ...;
const username = ...;
const response = {
"username": "...",
firstname: "...",
name: "...",
email: "...",
groups: []
};
return response;
};
I add a cognito Authorizer. With token, the result is OK and whithout the result is 403. is it OK for me.
exemple:
https://123456789.execute-api.eu-west-1.amazonaws.com/v1/user/me
return:
{
"username": "foobar",
"firstname": "foo",
"name": "bar",
"email": "foobar#gmail.com",
"roles": [
"Admin"
]
}
* with foobar if foobar is in JWT and return toto if toto is in JWT
Now, I want return username of user (from JWT). My event is empty:
"event": {},

Answer 1

const claims = event.requestContext.authorizer.claims;
const username = claims['cognito:username'];
before use this, I need use proxyLambda
and add this for the CORS (CORB):
const response = {
statusCode: 200,
headers: {
"Access-Control-Allow-Origin": "*"
},
body: JSON.stringify(r)
};
return response;
or other solution: i do not use proxyLamba but you configure this:
after, you need decode JWT in Lambda.
const jwtToken = event.params.header.Authorization;

Answer 2

I don't think return is doing what you expect. Try using callback. Detail here
Node.js runtimes support the optional callback parameter. You can use
it to explicitly return information back to the caller.
callback(Error error, Object result); Both parameters are optional.
error is an optional parameter that you can use to provide results of
the failed Lambda function execution. When a Lambda function succeeds,
you can pass null as the first parameter.
result is an optional parameter that you can use to provide the result
of a successful function execution. The result provided must be
JSON.stringify compatible. If an error is provided, this parameter is
ignored.
If you don't use callback in your code, AWS Lambda will call it
implicitly and the return value is null. When the callback is called,
AWS Lambda continues the Lambda function invocation until the event
loop is empty.
var AWS = require('aws-sdk');
const cognito = new AWS.CognitoIdentityServiceProvider({apiVersion: '2016-04-18'})
exports.handler = function(event, context, callback) => {
const token = ...;
const username = ...;
const response = {
"username": "...",
firstname: "...",
name: "...",
email: "...",
groups: []
};
callback(null, response);
};