Question: ETag support

[yubing24]

Do you consider supporting ETag and embed ETag value to the response header?

I know ETag calculation varies, so I would propose an interface function that accepts an entity (User or Group), and returns a string as ETag:

type IEtagCalculator interface {
    CalculateEtag(entity {}interface) string
}

This interface can be added to scim.ServerOption or scim.ServerArgs. This should allow supporting calculating ETag with one specific function

Client code will need to implement the ETag function. If not, the server should warn that ETag function is nil.

If you don't have plan to support ETag, would you be open to adding a SupportEtag field to ServiceProviderConfig so that the service configuration for ETag can be customized by client code?

[q-uint]

Thanks for raising this! ETags are indeed part of the SCIM spec (RFC 7644, Section 3.14), and we're open to contributions here.

The library already partially supports ETags:

• Resource handlers can populate Meta.Version, and the library sets the ETag HTTP response header from it (see handlers.go).
• This works for GET, POST, PUT, and PATCH responses.

What's currently missing:

1. ServiceProviderConfig hardcodes etag.supported to false with no way to configure it. Adding a SupportEtag field would be straightforward.
2. If-Match / If-None-Match conditional request handling: the library doesn't validate these headers or return 412 Precondition Failed / 304 Not Modified. Since version comparison logic is implementation-specific, this would likely need to be delegated to the resource handler.

Contributions for either or both of these are welcome!