Merge commit from fork

Added a dummy bcrypt hash to prevent user enumeration timing attacks in JSON authentication.

auth/json.go

@@ -14,6 +14,10 @@ import (
 // MethodJSONAuth is used to identify json auth.
 const MethodJSONAuth settings.AuthMethod = "json"
 
+// dummyHash is used to prevent user enumeration timing attacks.
+// It MUST be a valid bcrypt hash.
+const dummyHash = "$2a$10$O4mEMeOL/nit6zqe.WQXauLRbRlzb3IgLHsa26Pf0N/GiU9b.wK1m"
+
 type jsonCred struct {
 	Password  string `json:"password"`
 	Username  string `json:"username"`
@@ -52,7 +56,17 @@ func (a JSONAuth) Auth(r *http.Request, usr users.Store, _ *settings.Settings, s
 	}
 
 	u, err := usr.Get(srv.Root, cred.Username)
-	if err != nil || !users.CheckPwd(cred.Password, u.Password) {
+
+	hash := dummyHash
+	if err == nil {
+		hash = u.Password
+	}
+
+	if !users.CheckPwd(cred.Password, hash) {
+		return nil, os.ErrPermission
+	}
+
+	if err != nil {
 		return nil, os.ErrPermission
 	}