Supporting CORS using SAM

cors_handler.js

// cors_handler.js

const ALLOW_HEADERS = [
  'Content-Type',
  'X-Amz-Date',
  'Authorization',
  'X-Api-Key',
  'X-Amz-Security-Token'
];

const ALLOW_METHODS = [
  'GET',
  'OPTIONS',
  'POST'
];

const ALLOW_ORIGIN = '*';

export.preflight = (event, context, callback) => {
  callback({
    statusCode: 200,
    headers: {
      'Access-Control-Allow-Headers': ALLOW_HEADERS.join(','),
      'Access-Control-Allow-Methods': ALLOW_METHODS.join(','),
      'Access-Control-Allow-Origin': ALLOW_ORIGIN
    },
    body: ''
  });
};

// template.yaml
//
// Preflight:
//   Type: AWS::Serverless::Function
//   Properties:
//     Handler: cors_handler/preflight
//     Runtime: nodejs6.10
//     CodeUri: ./package.zip
//     Events:
//       OptionsPeople:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /people
//       OptionsPerson:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /people/{personId}
//       OptionsPlaces:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /places
//       OptionsPlace:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /places/{placeId}
//       OptionsThings:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /things
//       OptionsThing:
//         Type: Api
//         Properties:
//           Method: OPTIONS
//           Path: /things/{thingId}