Web3auth (mumbai chain) blocked by CORS

Technical Issue Reporting
#1

This was working fine for the past 2 weeks and it suddenly stopped working. The web3auth modal popups up but once I click to login the console.log error appears:

Access to fetch at 'https://rpc-mumbai.maticvigil.com/' from origin 'http://localhost:3031' 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. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

This is my code:

  const user = await Moralis.authenticate({
    provider: 'web3Auth',
    clientId: process.env.WEB3AUTH_CLIENTID,
    chainId: '0x13881',
  });
#2

Did you try with 127.0.0.1 instead of localhost?

#3

Yes it didn’t work with 127.0.0.1 either.
As well as my deployed app on vercel.

#4

Is that RPC url working now?

#5

Nope

Screen Shot 2022-05-07 at 10.41.11 AM
Screen Shot 2022-05-07 at 10.41.11 AM873×189 42.7 KB

#6

I mean if you try to use it directly as a RPC url for example to get latest block number

#7

it looks like https://rpc-mumbai.maticvigil.com/ doesn’t work for me either when I try to use it as a RPC url

#8

mmhh so any ideas how I can get web3auth to work then w/ mumbai?

#9

Try using another RPC from this page on the testnet tab.

#10

That makes sense to me however Moralis doesn’t expose the parameter to point to a different RPC in the Moralis.authenticate() function. https://rpc-mumbai.maticvigil.com/ seems to be set by default if you choose the Mumbai chain.

Screen Shot 2022-05-08 at 2.42.45 PM
Screen Shot 2022-05-08 at 2.42.45 PM767×782 75.1 KB

#11

it looks like something that web3auth provider can change

they could make an update for that

#12

Any updates? Mine just stopped working for seemingly the same reasons…

Access to fetch at ‘https://rpc-mumbai.maticvigil.com/’ from origin ‘’ 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. If an opaque response serves your needs, set the request’s mode to ‘no-cors’ to fetch the resource with CORS disabled.

#13

The problem is related to that RPC url that stopped working. We are looking to see if we can find a solution.

#14

Thanks. I talked to tech support on web3auth side and they said the same thing. This was suggested. https://docs.web3auth.io/api-reference/web/plugnplay#example

#15

The issue doesnt seem to be resolved. Is there any other way we are able to test moralis web3auth on mumbai chain?

#16

A temporarily solution for your local development is to change node_modules\moralis\lib\browser\Web3Connector\Web3AuthConnector.js so it uses another RPC:

// Build config
ethChainConfig = {
  chainNamespace: 'eip155',
  chainId: (0, _verifyChainId.default)(chainId)
}; // Build Web3Auth

to:

if (chainId === '0x13881') {
  ethChainConfig = {
    chainNamespace: 'eip155',
    chainId: (0, _verifyChainId.default)(chainId),
    rpcTarget: 'https://rpc-mumbai.matic.today'
  }; // Build Web3Auth

} else {
  ethChainConfig = {
    chainNamespace: 'eip155',
    chainId: (0, _verifyChainId.default)(chainId),
  }; // Build Web3Auth
}
1 Like
#17

Thanks for your help.
But I am not sure why it is still going ‘https://rpc-mumbai.maticvigil.com/’ instead of the stated rpcTarget.
It does not seem to enter the if statement.

#18

you changed that code directly in node modules in node_modules\moralis\lib\browser\Web3Connector\Web3AuthConnector.js ?

#19

Make sure you restart your app server. Also that change will only work on the browser side of things.

#20

Yes, i changed code directly in web3AuthConnector.js and restarted the app server.
Is there a way to console log so i am able to see the rpcTarget result?