Hello Abhner the platform provide some options out-of-the-box: Built-in, Active Directory and LDAP.

You can see more details here: https://success.outsystems.com/Evaluation/Security/02_Security_of_OutSystems_applications/01_What_identity_providers_can_be_used_in_OutSystems_apps

And to setup you can see more details here: 

• https://www.outsystems.com/help/servicestudio/9.0/Handling_security/Configuring_End-User_Authentication.htm
• https://success.outsystems.com/Evaluation/Lifecycle_Management/5_Identity_and_Access_Management

To customize and use your own Platfomr credentials you need to create your own UserProvider, the best way to do this is clone the Users and customize it. To clone Users eSpace follow the steps bellow:

1. Open any project go to Logic tab find Users and try to open it, when you do this, platform ask you to clone it.
2. Select Open a Clone button:
    
3. So you can give a name like MyUsers per example and publish.
4. Now you can customize action User_Login to use your platform, but you need after authenticating on your platform to create the user also in OutSystems Users so you can verify that it is done for LDAP and Active Directory:
   
5. At the end of your logic you should call the Login action to create a session for the user on the platform:
   
6. In your application you can select application name and change property User provider module to point to your own UserProvider like bellow:
7. 

Hope this helps.

No problem if this helps you remeber to mark as a solution in this thread.

Best regards!