fix: allow STS creds for admin accounts to add users (#11138)

Allow rotating creds with privileges to add users

fixes https://github.com/minio/console/issues/529

cmd/admin-handlers-users.go

@@ -373,23 +373,29 @@ func (a adminAPIHandlers) AddUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if cred.IsTemp() || cred.IsServiceAccount() {
+	// Not allowed to add a user with same access key as root credential
-		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAccountNotEligible), r.URL)
+	if owner && accessKey == cred.AccessKey {
+		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAddUserInvalidArgument), r.URL)
 		return
 	}
 
-	// Not allowed to add a user with same access key as root credential
+	if (cred.IsTemp() || cred.IsServiceAccount()) && cred.ParentUser == accessKey {
-	if owner && accessKey == cred.AccessKey {
+		// Incoming access key matches parent user then we should
+		// reject password change requests.
 		writeErrorResponseJSON(ctx, w, errorCodes.ToAPIErr(ErrAddUserInvalidArgument), r.URL)
 		return
 	}
 
 	implicitPerm := accessKey == cred.AccessKey
 	if !implicitPerm {
+		parentUser := cred.ParentUser
+		if parentUser == "" {
+			parentUser = cred.AccessKey
+		}
 		if !globalIAMSys.IsAllowed(iampolicy.Args{
-			AccountName:     cred.AccessKey,
+			AccountName:     parentUser,
 			Action:          iampolicy.CreateUserAdminAction,
-			ConditionValues: getConditionValues(r, "", cred.AccessKey, claims),
+			ConditionValues: getConditionValues(r, "", parentUser, claims),
 			IsOwner:         owner,
 			Claims:          claims,
 		}) {