Unable to verify SHA256 signature in go

I have been trying to verify a signature generated in Node with the go crypto package. The signature is generated from the createSig() function. Then in go I am verifying that with verifySig() but it always fails. These private/public keys are safe to share as they were generated for this example. I was able to run a verification in Node from the signature without an issue but I'm not sure what's happening in go to make it fail.

Generating signature in Node

function createSig() {
  const crypto = require("crypto");

  function fromBase64(base64) {
	return base64.replace(/=/g, "").replace(/\+/g, "-").replace(/\//g, "_");
  }

  const PRIVATE_KEY =
	"-----BEGIN PRIVATE KEY-----\nMIIBVQIBADANBgkqhkiG9w0BAQEFAASCAT8wggE7AgEAAkEAyX1juQ2AVhS5NdKl\nJL5g4A+fPLUUWh2Tq1+f0Z1rb1dpCZ+RXECJAdW4ocsl5n24QtmzD66Z/s1bs+B5\nOyD4KwIDAQABAkBqxbiXsrDkbNzsybBbtUsO0Rh4Chk729qKAQVnBf2NpRmz3KAf\nMXP5M9Wr9HlD1PT8WUUaYvGtabbbkXTFq+pBAiEA+T2Lja3seY2NUxsR0Qi211Ug\nKCd820+5Tjft1XMf1aECIQDO9FDm5asV3q60YvqpifSawiS2JH/DS7Whg4X0M64i\nSwIhAPaKTY/g+eim/6O0RCRspUhNeRifLt9VdiyMIGOilFvhAiAJxgH4FYqR2tVX\nUYFS9l/l2xtOusSJ3Y5zVTnDQZmMpwIhAMibeam8MvHMr3FjTqE5CwOgsg6zXiWZ\nFA9ZnEINP5jz\n-----END PRIVATE KEY-----";
  var message = "test";

  var signer = crypto.createSign("RSA-SHA256");
  signer.update(message);
  return fromBase64(signer.sign(PRIVATE_KEY, "base64"));
}

Verifying in go

func verifySig(message, signature string) (bool, error) {
	var key = "-----BEGIN PUBLIC KEY-----\nMFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAMl9Y7kNgFYUuTXSpSS+YOAPnzy1FFod\nk6tfn9Gda29XaQmfkVxAiQHVuKHLJeZ9uELZsw+umf7NW7PgeTsg+CsCAwEAAQ==\n-----END PUBLIC KEY-----"
	block, _ := pem.Decode([]byte(key))
	if block == nil {
		return false, errors.New("uh oh")
	}

	sh := crypto.SHA256.New()
	sh.Write([]byte(message))
	hashed := sh.Sum(nil)

	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
      return false, err
	}

	if pubKey, ok := pub.(*rsa.PublicKey); ok {
		err := rsa.VerifyPKCS1v15(pubKey, crypto.SHA256, hashed, []byte(signature))
		if err != nil {
            // THIS IS WHERE I END UP EVERY TIME
			return false, err
		}
        return true, nil
	}
}

Working Node verification:

function verifySig(message, signature) {

  const PUBLIC_KEY =
  "-----BEGIN PUBLIC KEY-----\nMFwwDQYJKoZIhvcNAQEBBQADSwAwSAJBAMl9Y7kNgFYUuTXSpSS+YOAPnzy1FFod\nk6tfn9Gda29XaQmfkVxAiQHVuKHLJeZ9uELZsw+umf7NW7PgeTsg+CsCAwEAAQ==\n-----END PUBLIC KEY-----";

  var verifier = crypto.createVerify("RSA-SHA256");
  verifier.update(message);

  // will return true
  return verifier.verify(PUBLIC_KEY, signature, "base64");
}

I think there are 2 issues with your code.

First: in NodeJs you encoded the signature using Base64 and secondly you converted the Base64 string to a "UrlSafe" Base64-encoded string.

Those two steps need to be reversed (I don't know if Go has a built-in "Url-safe Base64 decoding function") before you use the signature string as input for your verification in Go.