TenantInterceptor.cs

public class TenantInterceptor
{
    private const string TenantHeader = "x-tenant-id";
    private readonly RequestDelegate _next;

    public TenantInterceptor(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext httpContext)
    {
        if (httpContext.Request.Headers.TryGetValue(TenantHeader, out var tenantHeaders))
        {
            var tenantId = tenantHeaders.First();
            httpContext.Items[TenantHeader] = tenantId;
        }

        await _next(httpContext);
    }
}