Auth: Add option for case insensitive login (#49262)

* add case insensitive option

* treat id as case insensitive

* Users: Add integration tests for case insensitive querying

* Prefer config struct to global variable

* change key to case_insensitive_login

* impede conflicting users from logging in

* add tests for impeding user retrieval if conflicting

* nits and picks

Co-authored-by: gamab <gabi.mabs@gmail.com>

* Add check in transaction for conflicting user

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

* add update tests

* skip on mysql

* add custom messages for user admin view

Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

* nit: extra else

* linting mistake

Co-authored-by: gamab <gabi.mabs@gmail.com>
Co-authored-by: Gabriel MABILLE <gamab@users.noreply.github.com>

pkg/setting/setting.go

@@ -360,6 +360,7 @@ type Cfg struct {
 	// User
 	UserInviteMaxLifetime time.Duration
 	HiddenUsers           map[string]struct{}
+	CaseInsensitiveLogin  bool // Login and Email will be considered case insensitive
 
 	// Annotations
 	AnnotationCleanupJobBatchSize      int64
@@ -1354,6 +1355,8 @@ func readUserSettings(iniFile *ini.File, cfg *Cfg) error {
 	AutoAssignOrgRole = cfg.AutoAssignOrgRole
 	VerifyEmailEnabled = users.Key("verify_email_enabled").MustBool(false)
 
+	cfg.CaseInsensitiveLogin = users.Key("case_insensitive_login").MustBool(false)
+
 	LoginHint = valueAsString(users, "login_hint", "")
 	PasswordHint = valueAsString(users, "password_hint", "")
 	cfg.DefaultTheme = valueAsString(users, "default_theme", "")