Fix CORS “Response to preflight…” header not present with AWS API gateway and amplify

Question

I\'ve been struggling so long with the error below. I\'ve tried so many tutorials and stackoverflow answers and none of the solutions fixes my problem.

Answer 1

If Someone using serverless with nodejs and facing this issue of prelight with cors-policy, here is the simple solution ...

functions:
  externalHandler:
    handler: handler.handlerExport
    events:
      - http:
          path: handlerPath
          method: post
          cors:
            origin: '*' # <-- Specify allowed origin
            headers: # <-- Specify allowed headers
              - Content-Type
              - X-Amz-Date
              - Accept
              - Authorization
              - X-Api-Key
              - X-Amz-Security-Token
              - X-Amz-User-Agent
            allowCredentials: false

inside the handler file

if you are using express

...
const app = express();
app.use(function (req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Credentials", true);
  res.setHeader("Access-Control-Allow-Methods", "GET, POST, DELETE, OPTIONS");
  res.header(
    "Access-Control-Allow-Headers",
    "x-www-form-urlencoded, Origin, X-Requested-With, Content-Type, Accept, Authorization"
  );
  next();
});
...

or in general

  const response = {
    statusCode: 200,
    headers: {
      'Access-Control-Allow-Origin': '*',
      'Access-Control-Allow-Credentials': true,
    },
    body: JSON.stringify({
      product: product
    }),
  };

for more information refer serverless article