How to handle REST API error in a B2C custom policy?

Question

Problem description

I want to check if a user is a member of a particular group inside of my B2C custom policy.

Solutions I have tried

I am using MS Graph API to check this. I have tried to check with the following APIs

GET https://graph.microsoft.com/v1.0/groups/{groupObjectId}/members/{userObjectId}

This works well for positive cases (when a user is in the group), but when the user is not in the group, it returns a 404 status code, which is impossible to handle with a custom policy.

POST https://graph.microsoft.com/v1.0/users/{userObjectId}/checkMemberObjects

{
    "ids": [
        "groupObjectId"
    ]
}

This API returns a 200 status code in any case, and I can handle the response, but the userObjectId is dynamic, and I have to set SendClaimsIn to Url so that I cannot pass request body and send a POST request.

I have also tried to check the same thing with reversed API where the groupObjectId will be static and will not force me to use <Item Key="SendClaimsIn">Url</Item> .

POST https://graph.microsoft.com/v1.0/groups/{groupObjectId}/checkMemberObjects

{
    "ids": [
        "userObjectId"
    ]
}

But this returns 400 Bad Request with the following message

{
    "error": {
        "code": "Request_BadRequest",
        "message": "The object class referenced by given parameters is not valid for member link.",
        "innerError": {
            "date": "2022-09-08T13:13:11",
            "request-id": "71ab6e9f-059f-4b9c-b40b-69671f7a3f31",
            "client-request-id": "71ab6e9f-059f-4b9c-b40b-69671f7a3f31"
        }
    }
}

The question

An answer to any of the following questions will be counted as an answer and appreciated.

1. Is there a way to handle 404 status codes in custom policies? ( A likely question was answered in 2019, maybe it is possible now.)
2. How to make the third API work?
3. What would you recommend for checking a user's group membership using B2C custom policies?

Additional information

Currently, I am checking this based on this sample , but this is a bad solution as a user can be a member of many groups (including the needed one), but we are checking only with first three groups.

Answer 1

You could use query parameters to customize responses .

GET https://graph.microsoft.com/v1.0/groups/{groupObjectId}/members$filter=id eq '{userObjectId}'

Then check if @odata.count equals one and if so, the user with that particular userObjectId exists in that group.