The answer to this question is going to be difficult if I cannot see your design.
Firstly, WCAG explicitly states in 2.1 "Make all functionality available from a keyboard". This will obviously present a number of challenges when it comes to mouse drag and drop.
You can add ARIA attributes to your HTML to add keyboard interaction for drag and drop, but this is not a silver bullet to solve your problem for keyboard use. Only when you fully appreciate all the elements of your drag and drop can you begin to understand how you can support keyboard users.
In their book "Designing Web Interactions", Bill Scott & Theresa Neil identified 15 events for cuing the users during a drag and drop interaction, and each of these will need to consider an accessibility alternative:
- Page load
- Mouse Hover
- Mouse Down
- Drag Initiated
- Drag Leaves Original Location
- Drag Re-enters Original Location
- Drag Enters Valid Target
- Drag Exits Valid Target
- Drag Enters Specific Invalid Target
- Drag is Over No Specific Target
- Drag Hovers Over Valid Target
- Drag Hovers Over Invalid Target
- Drop Accepted
- Drop Rejected
- Drop on Parent Container
Not all of these event will be applicable to your drag and drop design, but hopefully you will now see the challenge that awaits you.Thinking about accessibility will cause you to approach design differently.
This article describes how to use ARIA attributes to make drag and drop work with a keyboard: https://dev.opera.com/articles/accessible-drag-and-drop/ (there is demo on this site so you can see it in action too), however, because there is a lot more to drop and drop, it might be simpler to re-think your design.
For example depending on your design, you can use copy & paste triggers from a menu, or place move buttons on the movable object for keyboard users, while mouse users can continue to use mouse drag and drop.