If you want to integrate with Marketo via the REST API, the best practice is to assign a user the API Only role and then create a custom service for use with ReST API. Here's how to create the API only user role.
From My Marketo, click Admin.
Under Security, click Users & Roles.
Click the Roles tab and then New Role.
Enter a Role Name, select the API access Permissions you want to give, and click Create.
It's always a good idea to only grant the minimum permissions required.
Okay, well done! Now let's create an API Only user.