Can I run Cognito in a Lambda function? - node.js

Question

I want to sign up users with Cognito in a Lambda function. However I am receiving "TypeError: fetch is not a function"
My code is basically step 3 in this. However I keep getting the above-mentioned error, even though I have node-fetch installed. From what I understand, the Cognito SDK makes use of fetch. So is this simply not possible? Will I need to spin up a Node server?
const AWS = require("aws-sdk");
const AmazonCognitoIdentity = require("amazon-cognito-identity-js");
//Configuring pool data of Cognito Identity Pool
const poolData = {
UserPoolId: "us-east-2_aCvZbFzeS",
ClientId: "4nv2krchr77pbrq3cpk0q0kknu"
};
const userPool = new AmazonCognitoIdentity.CognitoUserPool(poolData);
AWS.config.region = "us-east-2";
const attributeList = [];
attributeList.push(
new AmazonCognitoIdentity.CognitoUserAttribute({
Name: "email",
Value: "sampleEmail#gmail.com"
})
);
userPool.signUp(
"sampleEmail#gmail.com",
"SamplePassword123",
attributeList,
null,
function(err, result) {
if (err) {
console.log(err);
return;
}
const cognitoUser = result.user;
console.log("user name is " + cognitoUser.getUsername());
}
);
const data = JSON.parse(event.body);
const headers = {
"Access-Control-Allow-Origin": "*",
"Access-Control-Allow-Credentials": true
};
const response = {
statusCode: 200,
headers: headers,
"Content-Type": "application/json",
body: JSON.stringify(data.age)
};
callback(null, response);
};
//I keep receiving this error when attempting to hit the endpoint with Postman:
"errorMessage": "Uncaught error in your 'hello' handler",
"errorType": "TypeError",
"stackTrace": [
"TypeError: fetch is not a function"

Answer 1

You can definitely use Cognito from Lambda! Source: have done it.
You may not be able to use the AWS Cognito JS SDK from Lambda nicely, though.
The AWS Cognito JS SDK appears to be designed for client-side applications, where fetch is a built-in. You have installed node-fetch, but the SDK is not loading it because it doesn't think it needs to, because it is expecting it to be built-in.
I see two options:
If you aren't particularly attached to JS, you could use another language where you are confident that the library is designed and tested for server-side applications.
If you are attached to JS or have a large sunk cost, you could hack up the AWS Cognito JS SDK locally before deploying the code to Lambda to make it require node-fetch or otherwise make it functional server-side.
This thread has a good description of the same issue and some workarounds; probably the best one for you is:
global.fetch = require('node-fetch')
const AmazonCognitoIdentity = require('amazon-cognito-identity-js');
in your script, which should make it appear as a built-in to the SDK's code without hacking up the internals.