Don't use custom PBKDF2 function (#382)

models/user.go

@@ -25,6 +25,7 @@ import (
 	"github.com/Unknwon/com"
 	"github.com/go-xorm/xorm"
 	"github.com/nfnt/resize"
+	"golang.org/x/crypto/pbkdf2"
 
 	"code.gitea.io/git"
 	api "code.gitea.io/sdk/gitea"
@@ -361,7 +362,7 @@ func (u *User) NewGitSig() *git.Signature {
 
 // EncodePasswd encodes password to safe format.
 func (u *User) EncodePasswd() {
-	newPasswd := base.PBKDF2([]byte(u.Passwd), []byte(u.Salt), 10000, 50, sha256.New)
+	newPasswd := pbkdf2.Key([]byte(u.Passwd), []byte(u.Salt), 10000, 50, sha256.New)
 	u.Passwd = fmt.Sprintf("%x", newPasswd)
 }