Add API Token Cache

One of the issues holding back performance of the API is the problem of hashing.
Whilst banning BASIC authentication with passwords will help, the API Token scheme
still requires a PBKDF2 hash - which means that heavy API use (using Tokens) can
still cause enormous numbers of hash computations.

A slight solution to this whilst we consider moving to using JWT based tokens and/or
a session orientated solution is to simply cache the successful tokens. This has some
security issues but this should be balanced by the security issues of load from
hashing.

Related #14668

Signed-off-by: Andrew Thornton <art27@cantab.net>

custom/conf/app.example.ini

@@ -378,6 +378,10 @@ INTERNAL_TOKEN=
 ;;
 ;; Validate against https://haveibeenpwned.com/Passwords to see if a password has been exposed
 ;PASSWORD_CHECK_PWN = false
+;;
+;; Cache successful token hashes. API tokens are stored in the DB as pbkdf2 hashes however, this means that there is a potentially significant hashing load when there are multiple API operations.
+;; This cache will store the successfully hashed tokens in a LRU cache as a balance between performance and security.
+;SUCCESSFUL_TOKENS_CACHE_SIZE = 20
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -440,6 +440,7 @@ relation to port exhaustion.
     - spec - use one or more special characters as ``!"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~``
     - off - do not check password complexity
 - `PASSWORD_CHECK_PWN`: **false**: Check [HaveIBeenPwned](https://haveibeenpwned.com/Passwords) to see if a password has been exposed.
+- `SUCCESSFUL_TOKENS_CACHE_SIZE`: **20**: Cache successful token hashes. API tokens are stored in the DB as pbkdf2 hashes however, this means that there is a potentially significant hashing load when there are multiple API operations. This cache will store the successfully hashed tokens in a LRU cache as a balance between performance and security. 
 
 ## OpenID (`openid`)
 

models/models.go

@@ -17,6 +17,7 @@ import (
 
 	// Needed for the MySQL driver
 	_ "github.com/go-sql-driver/mysql"
+	lru "github.com/hashicorp/golang-lru"
 	"xorm.io/xorm"
 	"xorm.io/xorm/names"
 	"xorm.io/xorm/schemas"
@@ -234,6 +235,15 @@ func NewEngine(ctx context.Context, migrateFunc func(*xorm.Engine) error) (err e
 		return fmt.Errorf("sync database struct error: %v", err)
 	}
 
+	if setting.SuccessfulTokensCacheSize > 0 {
+		successfulAccessTokenCache, err = lru.New(setting.SuccessfulTokensCacheSize)
+		if err != nil {
+			return fmt.Errorf("unable to allocate AccessToken cache: %v", err)
+		}
+	} else {
+		successfulAccessTokenCache = nil
+	}
+
 	return nil
 }
 

models/token.go

@@ -14,8 +14,11 @@ import (
 	"code.gitea.io/gitea/modules/util"
 
 	gouuid "github.com/google/uuid"
+	lru "github.com/hashicorp/golang-lru"
 )
 
+var successfulAccessTokenCache *lru.Cache
+
 // AccessToken represents a personal access token.
 type AccessToken struct {
 	ID             int64 `xorm:"pk autoincr"`
@@ -52,6 +55,21 @@ func NewAccessToken(t *AccessToken) error {
 	return err
 }
 
+func getAccessTokenIDFromCache(token string) int64 {
+	if successfulAccessTokenCache == nil {
+		return 0
+	}
+	tInterface, ok := successfulAccessTokenCache.Get(token)
+	if !ok {
+		return 0
+	}
+	t, ok := tInterface.(int64)
+	if !ok {
+		return 0
+	}
+	return t
+}
+
 // GetAccessTokenBySHA returns access token by given token value
 func GetAccessTokenBySHA(token string) (*AccessToken, error) {
 	if token == "" {
@@ -66,17 +84,38 @@ func GetAccessTokenBySHA(token string) (*AccessToken, error) {
 			return nil, ErrAccessTokenNotExist{token}
 		}
 	}
-	var tokens []AccessToken
+
 	lastEight := token[len(token)-8:]
+
+	if id := getAccessTokenIDFromCache(token); id > 0 {
+		token := &AccessToken{
+			TokenLastEight: lastEight,
+		}
+		// Re-get the token from the db in case it has been deleted in the intervening period
+		has, err := x.ID(id).Get(token)
+		if err != nil {
+			return nil, err
+		}
+		if has {
+			return token, nil
+		}
+		successfulAccessTokenCache.Remove(token)
+	}
+
+	var tokens []AccessToken
 	err := x.Table(&AccessToken{}).Where("token_last_eight = ?", lastEight).Find(&tokens)
 	if err != nil {
 		return nil, err
 	} else if len(tokens) == 0 {
 		return nil, ErrAccessTokenNotExist{token}
 	}
+
 	for _, t := range tokens {
 		tempHash := hashToken(token, t.TokenSalt)
 		if subtle.ConstantTimeCompare([]byte(t.TokenHash), []byte(tempHash)) == 1 {
+			if successfulAccessTokenCache != nil {
+				successfulAccessTokenCache.Add(token, t.ID)
+			}
 			return &t, nil
 		}
 	}

modules/setting/setting.go

@@ -189,6 +189,7 @@ var (
 	PasswordComplexity                 []string
 	PasswordHashAlgo                   string
 	PasswordCheckPwn                   bool
+	SuccessfulTokensCacheSize          int
 
 	// UI settings
 	UI = struct {
@@ -840,6 +841,7 @@ func NewContext() {
 	PasswordHashAlgo = sec.Key("PASSWORD_HASH_ALGO").MustString("pbkdf2")
 	CSRFCookieHTTPOnly = sec.Key("CSRF_COOKIE_HTTP_ONLY").MustBool(true)
 	PasswordCheckPwn = sec.Key("PASSWORD_CHECK_PWN").MustBool(false)
+	SuccessfulTokensCacheSize = sec.Key("SUCCESSFUL_TOKENS_CACHE_SIZE").MustInt(20)
 
 	InternalToken = loadInternalToken(sec)