After a month I found some APIS which we can use to perform operation on user, like add/update/delete/get users, groups and roles.
base url: http://localhost:8080/business-central/rest/

[GET] /roles – Get a list of all roles

[GET] /users – Get a list of all users

[GET] /groups – Get groups

[GET] /users/{userName}/groups – Get a list of groups assigned to a user

[GET] /users/{userName}/roles — Gets a list of roles assigned to a user

[POST] /users Creates users

[Post] /users/{userName}/changePassword – Changes user password

[POST] /groups — Creates groups

[POST] /users/{userName}/groups – Overrides the user assigned groups with new values

[POST] /users/{userName}/roles – Overrides the user assigned roles with new values

[Post] /groups/{groupName}/permissions – Updates permissions for a group

[Post] /roles/{roleName}/permissions – Updates permissions for a role

[GET] /groups/{groupName}/permissions –Get all permissions for a group

[GET] /roles/{roleName}/permissions –Get all permissions for a role

[GET] /users/{userName}/permissions –Get all permissions for a user

[DELETE] /users/{userName} – Deletes a given user

[DELETE] /groups/{groupName} Deletes a given groups