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I am referring to Amazon documentation for the purpose of Customer Authentication. Currently, I am using LWA.

Steps I followed:

1. I enabled the Send Alexa Events Permission from the Alexa developer Console in Build > Permission page.




2. I took the grant code from the request in the cloudwatch logs which was sent when I logged in using Alexa companion app.

Example:-

    {

     "directive": {

         "header": {

             "messageId": "Example",

             "name": "AcceptGrant",

             "namespace": "Alexa.Authorization",

             "payloadVersion": "3"

         },

         "payload": {

            "grant": {

                "code": "Example2",

                "type": "OAuth2.AuthorizationCode"

            },

            "grantee": {

                "token": "Example3",

                "type": "BearerToken"

            }

         }

      }

    }

3. Permission Page under build on Alexa Developer console gave me client-Id and client-secret Which I used for making the post request to https://api.amazon.com/auth/o2/token.

Example:-

 POST /auth/o2/token HTTP/l.l

 Host: api.amazon.com

 Content-Type: application/x-www-form-urlencoded;charset=UTF-8 

 grant_type=authorization_code&code=&client_id=&client_secret=

I passed the code,client_id, and client_secret in the above example and made the post request to this URL https://api.amazon.com/auth/o2/token

4. I tried using x-www-form-urlencoded;charset=UTF-8 and also JSON for the Content-Type.

I followed the step given in the above documentation and I am stuck on the error ( 401 Unauthorized ):

{

    "error_description": "The request has an invalid grant parameter : code",

    "error": "invalid_grant"

}

I tried implementing it using Python code and Postman both. Ending up with the Same above error scenario.

Here is a sample code to help you and others who are looking to send events to alexa gateway.

const AWS = require('aws-sdk');

AWS.config.update({region: 'eu-west-1'});



// Create the DynamoDB service object

const ddb = new AWS.DynamoDB({ apiVersion: 'latest' });

const doc = new AWS.DynamoDB.DocumentClient({

            convertEmptyValues: true,

            service: ddb

        });        



// Using 'request' for http POST and GET request.

// https://www.npmjs.com/package/requests

// npm install --save requests 

const r = require('request');



//Handle Authorization. Call this method from your lambda handler whenever you get Alexa.Authorization message. You will get this message only when you select permission to 

//send events in your Smart Home Skill.

//Access to Event gateway allows you to enable Proactive Device Discovery and 

//Proactive State Reporting in your skill

//More information on Alexa.Authorization can be found on https://developer.amazon.com/docs/device-apis/alexa-authorization.html

function handleAuthorization(request, context, user) {  



    //Even when you are using your own authentication, the url below will still

    //point to amazon OAuth token url. The token you obtain here has to be stored

    //separately for this user. Whenever sending an event to alexa event gateway you will

    //require this token.

    //URL below is for EU server. Look at following documentation link to identify correct url

    //for your system.

    //https://developer.amazon.com/docs/smarthome/send-events-to-the-alexa-event-gateway.html

    var url = "https://api.amazon.com/auth/o2/token";

    var body = {

        grant_type : 'authorization_code',

        code : request.directive.payload.grant.code,

        client_id : 'your client id from permissions page on developer portal where you enable alexa events. This is id different than one you specify in account linking settings',

        client_secret : 'client secret from permissions page'

    }



    //https://developer.amazon.com/docs/smarthome/authenticate-a-customer-permissions.html

    r.post({

      url:     url,

      form :  body

    }, function(error, response, b){    

        if (error) { return console.log(error); }

        var body = JSON.parse(b);

        var params = {

          TableName: 'Devices',

          Item: {

            'id' : user,

            'auth_token' : body.access_token,

            'refresh_token' : body.refresh_token

          }

        }

        log("DEBUG:", "Authorization Body", JSON.stringify(body));

        log("DEBUG:", "Authorization Response", JSON.stringify(response));

        log("DEBUG:", "Database Params", JSON.stringify(params));



        // Call DynamoDB to add the item to the table

        var putObjectPromise = doc.put(params).promise();

        //Store auth_token and refresh_token in database. We will need these

        //while sending events to event gateway.

        //Send a success response.

        putObjectPromise.then(function(data) {

            var response = {

              event: {

                header: {

                  messageId: request.directive.header.messageId,

                  namespace: "Alexa.Authorization",

                  name: "AcceptGrant.Response",

                  payloadVersion: "3"

                },

                "payload": {

                }

              }

            };



            context.succeed(response);

        }).catch(function(err) {

            //TODO - Add a Authorization error response JSON here.      

            console.log(err);

        });                         

    });                   

}