create-react-app proxy request fails with 404 when backend is hosted on Azure

create-react-app use WebPackDevServer which uses https://github.com/chimurai/http-proxy-middleware#options

So you can use all the options from the same

Now one key header that is import in such cases of externally hosted server is host. This at times can issues if not correct, see below example

Websocket works on EC2 url but not on ElasticBeanstalk URL

Next is the cookies might be associated with localhost, i checked and they should go without any modification. But you might want to use the cookieDomainRewrite: "" option as well

So the final config I would use is below

"proxy":{
   "/api/*":{
   "target":"https://mytestbackend.azurewebsites.net",
   "secure":false,
      "headers": {
        "host": "mytestbackend.azurewebsites.net"
      },
      "cookieDomainRewrite": ""
  } 
}

Also on your client you want to use the withCredentials:true

let userinfo =await axios.get('/api/secured/userinfo',{withCredentials:true});