How to assign application role to user in azure active directory using graph api

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Azure

active-directory

Hi,

Here is what I did.
I have created an application with Organizational Sign in and I am adding the Employee to the Active Directory using Graph API when ever new Employee gets created in the system.Till then Everything is fine.Now I have added Application Specific Roles by editing Manifest file and Assign the User a role like Approver.now am able to get the role as part of the reponse.

Here is What I want to achieve
But How to add the roles to the user while creating or Updating the User role.I have seen we have to go with AppRoleAssignment.But with that I am not Sure whats the object ID and Other parameters.I have searched manytime even in MS reference they have shown how to read roles not add roles.can you guys help me out in ading the roles to the user?