node.js - Proper request template mapping or process in order to upload a photo to s3 using Serverless Framework

Question

I am using Serverless Version 1.0.0 and Node Version 5.7.1

I have an endpoint for updating a photo of a table in a mysql database. So prior to inserting the said photo, i am uploading the formdata i get from the browser to s3, and then update the photo url using the return image url.

The problem is i don't know what is the proper way to define the request mapping template in serverless.yml so that i could extract the photo, AND the path parameters AND the $context variable for the principal id

Here is my current serverless.yml function definition

updateBoardPhoto:
  handler: handler.updateBoardPhoto
  events:
    - http:
       path: boards/{boardId}/photo
       method: PUT
       integration: lambda
       parameters:
         headers:
           Authorization: false
         body:
           photo: true
         paths:
           boardId: true
       request:
         passThrough: WHEN_NO_TEMPLATES
         template:
           multipart/form-data: '{"principalId" : "$context.authorizer.principalId", "body" : $input.json("$"), "boardId": "$input.params(''boardId'')"'

Now here is the handler i have:

function updateBoardPhoto(event, context, callback) {
var photo = event.body.photo;
var boardId = event.boardId;
var principal = utils.processPrincipalId(event.principalId);

var s3FileName = randomstring.generate(10) + ".jpg";
var s3 = new AWS.S3();
s3.putObject({
    Bucket: config.UPLOAD_BUCKET,
    Key: s3FileName,
    Body: photo,
    ACL: 'public-read',
}, function (err, data) {
    if (err) {
        throw err;
    } else {
        console.log(data);
        context.succeed(data);
    }
});

Attempt 1

I tried to use WHEN_NO_TEMPLATES passthrough option, and defined no template but i only get the photo buffer input variable, and no boardId. BUT i successfully upload the photo to s3.

request:
  passThrough: WHEN_NO_TEMPLATES

// event variable i get:
{ photo: <Buffer 89 50 4e 47 0d 0a 1a 0a 00 00 00 0d 49 48 44 52 00 00 02 1c 00 00 00 ac 08 06 00 00 00 30 ab 75 20 00 00 00 19 74 45 58 74 53 6f 66 74 77 61 72 65 00 ... >,

isOffline: true, stageVariables: {} }

Attempt 2

Using the ff request definition:

request:
  passThrough: WHEN_NO_MATCH
  template:
    multipart/form-data: '{"principalId" : "$context.authorizer.principalId", "body" : $input.json("$"), "boardId": "$input.params(''boardId'')"'

// event variable i get
{ isOffline: true, stageVariables: {} }

I see no variables in my event variable at all! No photo, nor boardId.

Can anyone tell me what i'm doing wrong? I am using postman to test.