PluralKit/PluralKit.API/Authentication/AuthExt.cs

using System.Security.Claims;

using PluralKit.Core;

namespace PluralKit.API;

public static class AuthExt
{
    public static SystemId CurrentSystem(this ClaimsPrincipal user)
    {
        var claim = user.FindFirst(PKClaims.SystemId);
        if (claim == null) throw new ArgumentException("User is unauthorized");

        if (int.TryParse(claim.Value, out var id))
            return new SystemId(id);
        throw new ArgumentException("User has non-integer system ID claim");
    }

    public static LookupContext ContextFor(this ClaimsPrincipal user, PKSystem system)
    {
        if (!user.Identity.IsAuthenticated) return LookupContext.API;
        return system.Id == user.CurrentSystem() ? LookupContext.ByOwner : LookupContext.API;
    }

    public static LookupContext ContextFor(this ClaimsPrincipal user, PKMember member)
    {
        if (!user.Identity.IsAuthenticated) return LookupContext.API;
        return member.System == user.CurrentSystem() ? LookupContext.ByOwner : LookupContext.API;
    }
}