See: https://github.com/golang/go/blob/master/src/crypto/x509/x509.go#L1136

The error returned when unmarshmaling a key-id reads x509: trailing data after X.509 authority key-id. However, this is not the authority-key id, it is the key-id.

Instead it should read x509: trailing data after X.509 key-id

It looks like someone copied and pasted the error from here (https://github.com/golang/go/blob/master/src/crypto/x509/x509.go#L1102) without making the needed change to the text.