The code comment for rsa_utils.go says it's for a PKCS1 or PKCS8 public key (ParseRSAPublicKeyFromPEM parses a PEM encoded PKCS1 or PKCS8 public key ParseRSAPublicKeyFromPEM parses a PEM encoded PKCS1 or PKCS8 public key), but the function uses x509.ParsePKIXPublicKey instead. I was unable to get a PKCS1 public key despite the code comment, and basically just copied the entire function and swapped it from x509.ParsePKIXPublicKey to x509.ParsePKCS1PublicKey, which works. I am not clear but it seems that it's not matching the code comment and it took me quite some time to figure out why I couldn't parse my RSA Public Key (it wasn't accepted on jwt.io).

I suspect that the problem is not with the code comment, but with the implementation. Or am I doing something wrong that the parsing of a pem with PKCS1 encoding doesn't work using x509.ParsePKIXPublicKey but does work with x509.ParsePKCS1PublicKey?

// ParseRSAPublicKeyFromPEM parses a PEM encoded PKCS1 or PKCS8 public key
func ParseRSAPublicKeyFromPEM(key []byte) (*rsa.PublicKey, error) {
	var err error

	// Parse PEM block
	var block *pem.Block
	if block, _ = pem.Decode(key); block == nil {
		return nil, ErrKeyMustBePEMEncoded
	}

	// Parse the key
	var parsedKey interface{}
	if parsedKey, err = x509.ParsePKIXPublicKey(block.Bytes); err != nil {
		if cert, err := x509.ParseCertificate(block.Bytes); err == nil {
			parsedKey = cert.PublicKey
		} else {
			return nil, err
		}
	}

If we compare to

	if parsedKey, err = x509.ParsePKCS1PrivateKey(block.Bytes); err != nil {
		if parsedKey, err = x509.ParsePKCS8PrivateKey(block.Bytes); err != nil {
			return nil, err
		}
	}