Various fixes in login sources (#10428) (#10429)

Co-authored-by: guillep2k <18600385+guillep2k@users.noreply.github.com>

modules/auth/pam/pam.go

@@ -13,7 +13,7 @@ import (
 )
 
 // Auth pam auth service
-func Auth(serviceName, userName, passwd string) error {
+func Auth(serviceName, userName, passwd string) (string, error) {
 	t, err := pam.StartFunc(serviceName, userName, func(s pam.Style, msg string) (string, error) {
 		switch s {
 		case pam.PromptEchoOff:
@@ -25,12 +25,14 @@ func Auth(serviceName, userName, passwd string) error {
 	})
 
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	if err = t.Authenticate(0); err != nil {
-		return err
+		return "", err
 	}
 
-	return nil
+	// PAM login names might suffer transformations in the PAM stack.
+	// We should take whatever the PAM stack returns for it.
+	return t.GetItem(pam.User)
 }