How do I rename a user with the Google Admin SDK Directory API?

In the old Provisioning API, we were able to rename user accounts. I don't see a pertinent parameter in the new Directory API documentation which would allow for renaming of a user account. Is this still possible?

https://developers.google.com/admin-sdk/directory/v1/reference/users/update

I have a feeling it may be as simple as updating the primaryEmail field to the new username but I'd like clarification.

You guess it right. It is just as simple as changing the primaryEmail field. Here is my example below:

Let's say I am a reseller from reseller.com, and I have a resold domain called resold.com. Currently, I have one user created in my resold domain with the email address emily@resold.com. I am going to update it to happy@resold.com. Note: I am using my reseller reseller.com's credential.

PUT /admin/directory/v1/users/emily@resold.com

{
 "primaryEmail": "happy@resold.com"
}

HTTP/1.1 200 OK

{
 "kind": "admin#directory#user",
 "id": "XXXX",
 "primaryEmail": "happy@resold.com",
 "name": {
  "givenName": "Emily",
  "familyName": "Lam",
  "fullName": "Emily Lam"
 }