Potential alternative to the new "Operation-Location" header

ref: https://github.com/Microsoft/api-guidelines/blob/master/Guidelines.md#1321-put

For long running operations that return 202, it is suggested to use Operation-Location to refer to a resource that can be monitored to determine when the requested operation is complete. Although, not explicitly specified by the HTTP spec, it is common practice to use the Location header to point to this status monitoring resource. See RFC7240 and RESTful Web Services Cookbook

It would seem prudent to follow common practice and avoid creating a new non-standard header for something that is commonly done.

For the hybrid scenario where the Location header is used to refer to the partially created resource and the Operation-Location header is used to point to the status resource, an alternative would be the following response:

HTTP/1.1 202 Accepted
Location: https://api.contoso.com/v1.0/operations/123
Content-Location: https://api.contoso.com/v1.0/databases/db1
{
  "databaseName": "db1",
  "color": "red",
  "Status": "Provisioning",
  [ … other fields for "database" …]
}

This approach is consistent with it's use of 202 to indicate that the creation process has not completed. It continues to use the Location header to indicate the location of the status monitoring resource. However, it also uses the Content-Location header to indicate that there is a response body that represents the current state of the resource being created and provides a URL to the final destination of the resource.

This approach provides equivalent functionality but doesn't require inventing a new header, it follows current common practices and it avoids having to impose the rules that the hybrid 201 must a have a
body, and it must indicate that it is incomplete, and that 202 responses shouldn't return a body.

Start with Guidelines.md section 13.2.1 and review the linked RFC7240 section and RESTful Web Services Cookbook reference. Compare the proposed Location and Content-Location response with the existing guidance; done means the guideline decision and any resulting text change are clearly resolved.