Authentication

Hi,

I want to bypass the Moodle login page (ABC users).
Now I login into my Moodle, I have integrated three Logins, such as ABC, DEF, GHI.
ABC - We are fetching data(USER CREDENTIALS) through API.
DEF - We are fetching data(USER CREDENTIALS) through API.
GHI - We are fetching data through Active Directory.
Here is what is happening. ABC has its own portal too. Whenever a Course is created in Moodle, we give the course URL to put it on the ABC portal. When they want to access the Moodle course, they click on the link and redirected to the Moodle login page. They insert their credentials and take a course.
Now, we want to bypass the Moodle login page for ABC users.
Please let me know what you use in this case.