No 'Access-Control-Allow-Origin' header is present on the requested resource with CORS module enabled - express

Question

I am trying to get CORS working on my AWS Lambda server using Serverless. Right now I have two sub-domains (api.site.co and app.site.co).
In my app.js file on Express, I have installed CORS and enabled it like such:
app.use(
cors({
origin: 'https://app.site.co',
optionsSuccessStatus: 200,
}),
);
app.options('*', cors());
And then using the Axios module in React, I make this call:
axios
.post('/users/register', user)
.then(res => history.push('/login'))
.catch((err) => {
dispatch({
type: GET_ERRORS,
error: err.response.data,
});
});
Also, in my app.js file for the client app:
axios.defaults.baseURL = 'https://api.site.co';
When submitting any request, I receive this error:
Access to XMLHttpRequest at 'https://api.site.co/users/register' from origin 'https://app.site.co' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource.
So, far I have also tried changing my CORS configuration to:
app.use(cors());
app.options('*', cors());
But I am still getting the same error.
Any suggestions on how to address this?

Answer 1

Looks like there is a typo:
https://app.site.co/users/register => https://api.site.co/users/register
You're making a request to https://api.site.co but your configuration specifies https://app.site.co

Answer 2

This was a problem with the AWS Lambda Serverless setup. I needed to add
functions:
app:
handler: app.handler
events:
- http:
path: /
method: any
cors:
origin: 'https://app.site.co'
- http:
path: '{proxy+}'
method: any
cors:
origin: 'https://app.site.co'
So that it would allow CORS requests when proxying to the Express middleware.