How do I trust a self signed certificate from an electron app?

Try this if 'certificate-error' event doesn't work:

if (process.env.NODE_ENV === 'DEV') {
  process.env.NODE_TLS_REJECT_UNAUTHORIZED = 0;
}

Subscribe to the certificate-error event emitted by the app module and verify your self signed cert in the event handler.

It appears that you can also configure this on the BrowserWindow side of your electron startup script via setCertificateVerifyProc(). I couldn't get any of the other above methods to work, at least in Electron 10.4.4.

e.g.

var win = new BrowserWindow({
    ...
});

win.webContents.session.setCertificateVerifyProc((request, callback) => {
    var { hostname, certificate, validatedCertificate, verificationResult, errorCode } = request;

    // Calling callback(0) accepts the certificate, calling callback(-2) rejects it.
    if (isNotMyCertificate(certificate)) { callback(-2); return; }

    callback(0);
  });

Where isNotMyCertificate() verifies that the data in certificate is yours. console.log() it to discover the certificate structure. It gives you a bit more control over security than blanket allowing all certificates.

See setCertificateVerifyProc() in https://www.electronjs.org/docs/api/session#sessetcertificateverifyprocproc for more details.

You need to put the following code into your "shell" (core electron init) file:

// SSL/TSL: this is the self signed certificate support
app.on('certificate-error', (event, webContents, url, error, certificate, callback) => {
    // On certificate error we disable default behaviour (stop loading the page)
    // and we then say "it is all fine - true" to the callback
    event.preventDefault();
    callback(true);
});

This would allow insecure (invalid) certificates like self-signed one.

⚠ Please note that this is NOT a secure way of connecting to the server.

For more, check the documentation:
https://electron.atom.io/docs/api/app/#event-certificate-error