InvalidSignatureException from POST request

Question

I have a Lambda function that handles reading data from a file(stored inside S3 bucket) as well as inserting data to a Dynamodb table. This Lambda function is exposed as a REST endpoint using API gateway. The function accepts GET request as well as POST request. I'm making GET/POST requests from my REACT project using axios and aws4(for signing) libraries. GET request is to read data from a file stored inside S3 and it works just fine. And POST request is for inserting data into Dynamodb table. However, it doesn't work and AWS returns InvalidSignatureException error as a respond. This is an excerpt of my code :

createAWSSignedRequest(postData) {

    let request = {};

    if (postData) {
        request = {
            host: process.env.AWS_HOST,
            method: 'POST',
            url: process.env.AWS_URL,
            path: process.env.AWS_PATH,
            headers: {
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(postData)
        }
    } else {
        request = {
            host: process.env.AWS_HOST,
            method: 'GET',
            url: process.env.AWS_URL,
            path: process.env.AWS_PATH
        }

    }


    let signedRequest = aws4.sign(request, {
        secretAccessKey: process.env.AWS_SECRET_KEY,
        accessKeyId: process.env.AWS_ACCESS_KEY
    });

    return signedRequest;

}

This is how GET request is made :

let signedRequest = this.createAWSSignedRequest('GET');

axios(signedRequest)
        .then(response => {



        })
        .catch((error) => {
            console.log("error",error);
        });

This is how POST request is made :

    const data = {
            uuid: "916b7d90-0137-11e8-94e6-116965754e23", //just a mock value
            date : "22/jan/2018",
            user_response: [
                         {
                            question:"this is quesiton1",
                            choice:"user selected A"
                         },
                         {
                            question:"this is quesiton2",
                            choice: "user selected b"
                         },
                         {
                            question:"this is quesiton3",
                            choice: "user selected C"
                         }
                ]
        };



    let signedRequest = this.createAWSSignedRequest(data);



    axios(signedRequest)
        .then(response => {

           ......

        })
        .catch((error) => {

            console.log("error",error);
        });

As you can see, the code for both GET and POST requests are exactly the same (except payload and method type). I'm singing with the same secret access key and access key id for both requests. I'm not sure why one request results in "InvalidSignatureException" when the other doesn't. Can anyone shed a light on this issue for me.

Thanks

Answer 1

After having discussion with AWS4 lib developer, I figured out what I did wrong. AWS4 uses "body" as a payload attribute to compute signature. However, Axios uses "data" attribute as payload. My mistake was only setting either one of them. So when I set just "data" attribute, the payload was present in the request and content-length is computed correctly. However, the signature was incorrect since the payload was not taken into consideration when computing signature. When I set just "body", payload was not present in the request because Axios does not use "body" attribute for payload. The solution is to set both attributes with payload. I hope this helps to anyone who are having the same issue I have.