Fix various permission & login related bugs (#36002)

Permission & protection check:

- Fix Delete Release permission check
- Fix Update Pull Request with rebase branch protection check
- Fix Issue Dependency permission check
- Fix Delete Comment History ID check

Information leaking:

- Show unified message for non-existing user and invalid password
    - Fix #35984
- Don't expose release draft to non-writer users.
- Make API returns signature's email address instead of the user
profile's.

Auth & Login:

- Avoid GCM OAuth2 attempt when OAuth2 is disabled
    - Fix #35510

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/auth/auth.go

@@ -5,6 +5,7 @@
 package auth
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"regexp"
@@ -40,6 +41,20 @@ var globalVars = sync.OnceValue(func() *globalVarsStruct {
 	}
 })
 
+type ErrUserAuthMessage string
+
+func (e ErrUserAuthMessage) Error() string {
+	return string(e)
+}
+
+func ErrAsUserAuthMessage(err error) (string, bool) {
+	var msg ErrUserAuthMessage
+	if errors.As(err, &msg) {
+		return msg.Error(), true
+	}
+	return "", false
+}
+
 // Init should be called exactly once when the application starts to allow plugins
 // to allocate necessary resources
 func Init() {