fix a crash in base64 buffer pool (#8925)

looks like 1024 buffer size is not enough in
all situations, use 8192 instead which
can satisfy all the rare situations that
may arise in base64 decoding.

cmd/jwt/parser.go

@@ -57,7 +57,7 @@ var (
 func init() {
 	base64BufPool = sync.Pool{
 		New: func() interface{} {
-			buf := make([]byte, 1024)
+			buf := make([]byte, 8192)
 			return &buf
 		},
 	}