Compare session variables to hardcoded values in permissions

I have in my system multiple different groups that users can be related to, these are stored in session variables. Different database tables often are relevant to a certain set of groups.
Currently, session variables can only be compared to data in the table in the permissions section. It would help us a long way if there were a way to compare them to a hardcoded value.
For instance if you could define the row level security of a table as follows
{
"x-hasura-group-id": {
"_eq": "groupA"
}
}
or as
{
"x-hasura-group-id": {
"_in": ["groupA","groupC"]
}
}

Thanks for the help

The issue names no implementation files, tests, or entry points. Start by tracing Hasura permission handling for session-variable comparisons and compare the requested _eq and _in constant forms with current expression behavior; done means both examples are supported and covered by tests.

Written by the indexing model from the issue text.