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

common/auth/internal/service.go

 // Copyright 2015 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 internal
 
 import (
         "crypto/sha1"
         "encoding/hex"
         "fmt"
         "io/ioutil"
 
         "golang.org/x/net/context"
         "golang.org/x/oauth2"
         "golang.org/x/oauth2/google"
         "golang.org/x/oauth2/jwt"
 
-        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
+        "github.com/luci/luci-go/common/retry/transient"
 )
 
 type serviceAccountTokenProvider struct {
         jsonKey []byte
         path    string
         scopes  []string
 }
 
 // NewServiceAccountTokenProvider returns TokenProvider that uses service
 // account private key (on disk or in memory) to make access tokens.
@@ skipping 50 matching lines @@
 
 func (p *serviceAccountTokenProvider) MintToken(ctx context.Context, base *oauth2.Token) (*oauth2.Token, error) {
         cfg, err := p.jwtConfig(ctx)
         if err != nil {
                 logging.Errorf(ctx, "Failed to load private key JSON - %s", err)
                 return nil, ErrBadCredentials
         }
         switch newTok, err := grabToken(cfg.TokenSource(ctx)); {
         case err == nil:
                 return newTok, nil
-        case errors.IsTransient(err):
+        case transient.Tag.In(err):
                 logging.Warningf(ctx, "Error when creating access token - %s", err)
                 return nil, err
         default:
                 logging.Warningf(ctx, "Invalid or revoked service account key - %s", err)
                 return nil, ErrBadCredentials
         }
 }
 
 func (p *serviceAccountTokenProvider) RefreshToken(ctx context.Context, prev, base *oauth2.Token) (*oauth2.Token, error) {
         // JWT tokens are self sufficient, there's no need for refresh_token. Minting
         // a token and "refreshing" it is a same thing.
         return p.MintToken(ctx, base)
 }