handling decoding pem error (#1192)

Author: MrBTTF

Diff for: AUTHORS

@@ -92,6 +92,7 @@ Thomas Wodarek <wodarekwebpage at gmail.com>
 Tim Ruffles <timruffles at gmail.com>
 Tom Jenkinson <tom at tjenkinson.me>
 Vladimir Kovpak <cn007b at gmail.com>
+Vladyslav Zhelezniak <zhvladi at gmail.com>
 Xiangyu Hu <xiangyu.hu at outlook.com>
 Xiaobing Jiang <s7v7nislands at gmail.com>
 Xiuming Chen <cc at cxm.cc>

Diff for: auth.go

@@ -15,6 +15,7 @@ import (
 	"crypto/sha256"
 	"crypto/x509"
 	"encoding/pem"
+	"fmt"
 	"sync"
 )
 
@@ -371,7 +372,10 @@ func (mc *mysqlConn) handleAuthResult(oldAuthData []byte, plugin string) error {
 							return err
 						}
 
-						block, _ := pem.Decode(data[1:])
+						block, rest := pem.Decode(data[1:])
+						if block == nil {
+							return fmt.Errorf("No Pem data found, data: %s", rest)
+						}
 						pkix, err := x509.ParsePKIXPublicKey(block.Bytes)
 						if err != nil {
 							return err