[errors] de-specialize Transient in favor of Tags.

tokenserver/appengine/impl/utils/tokensigning/inspector.go

 // Copyright 2017 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package tokensigning
 
 import (
         "crypto/x509"
         "encoding/base64"
         "fmt"
         "strings"
 
         "github.com/golang/protobuf/proto"
         "golang.org/x/net/context"
 
         "github.com/luci/luci-go/common/clock"
-        "github.com/luci/luci-go/common/errors"
+        "github.com/luci/luci-go/common/retry/transient"
         "github.com/luci/luci-go/server/auth/signing"
 )
 
 // Inspector knows how to inspect tokens produced by Signer.
 //
 // It is used by Inspect<something>Token RPCs (available only to admins). It
 // tries to return as much information as possible. In particular, it tries to
 // deserialize the token body even if the signature is no longer valid. This is
 // useful when debugging broken tokens.
 //
@@ skipping 118 matching lines @@
                 return ""
         }
 }
 
 // checkSignature verifies the signature of the token.
 //
 // Returns "" if the signature is correct, or an invalidity reason if it is not.
 func (i *Inspector) checkSignature(c context.Context, unwrapped *Unwrapped) (string, error) {
         certsBundle, err := i.Certificates.Certificates(c)
         if err != nil {
-                return "", errors.WrapTransient(err)
+                return "", transient.Tag.Apply(err)
         }
         cert, err := certsBundle.CertificateForKey(unwrapped.KeyID)
         if err != nil {
                 return fmt.Sprintf("invalid signing key - %s", err), nil
         }
         withCtx := prependSigningContext(unwrapped.Body, i.SigningContext)
         err = cert.CheckSignature(x509.SHA256WithRSA, withCtx, unwrapped.RsaSHA256Sig)
         if err != nil {
                 return fmt.Sprintf("bad signature - %s", err), nil
         }
         return "", nil
 }