CORS error

Question

Any guide to setting up nginx reverse proxy for the backend server not core I keep on getting bombarded by cors errors

rp · Answer

hey < sdekna> to solve CORS error you should use a cors middleware for your application we have docs for this in our quick setup > backend section

sdekna · Answer

I am using an express backend with nginx reverse proxy to it This is my backend code https pastebin com 7dBmP2XC My nginx reverse proxy conf https pastebin com MJRvxJUZ I am using `supertokens web js` I am getting this error ``` Access to fetch at https API ENDPOINT signin $$ or sign up $$ from origin https FRONTEND DOMAIN has been blocked by CORS policy No Access Control Allow Origin header is present on the requested resource If an opaque response serves your needs set the request s mode to no cors to fetch the resource with CORS disabled ``` If I make a signup request it actually registers the user but I get the above error In the dashboard I see the new user and if I try to signup again with the same email I do get a proper response saying the email is already registered If I make a signin request I get the error above For reference I am using sveltekit in the frontend

rp · Answer

whats the status code of the response in chrome Also how have you added the CORS middleware in your express app is it before or after the supertokens middleware

sdekna · Answer

`ERR FAILED 502` I added it before the middlewear you may check the code here https pastebin com 7dBmP2XC

rp · Answer

hmm Does it work without the nginx in front

sdekna · Answer

yes but then I have to change everything to `http` instead of `https`

sdekna · Answer

and also if I call it from my production domain it gives me an error asking me to use https instead so basically I can only use it in http environment like dev

rp · Answer

right Im not sure if nginx is doing something to strip away the CORS headers this you will have to check on your own since it s out of scope of supertokens really

sdekna · Answer

sure any docs or blogs on setting up any reverse proxy to the backend api

sdekna · Answer

or somewhere to get me to start on solving this

rp · Answer

we don t have that Sorry

rp · Answer

oh right ok

rp · Answer

if you are getting 502 it means that the nginx is rejecting the response cause of long header length

rp · Answer

See this https www cyberciti biz faq nginx upstream sent too big header while reading response header from upstream

sdekna · Answer

many thanks for the help

sdekna · Answer

indeed this was the solution I needed to add this to my nginx conf ``` proxy busy buffers size 512k proxy buffers 4 512k proxy buffer size 256k ``` Many thanks for the help

rp · Answer

awesome