public class AddRequiredHeaderParameter : IOperationFilter
{
    public void Apply(Operation operation, SchemaRegistry schemaRegistry, ApiDescription apiDescription)
    {
        if (operation.parameters == null)
            operation.parameters = new List();

        operation.parameters.Add(new Parameter
        {
            name = "MyHeaderField",
            @in = "header",
            type = "string",
            description = "My header field",
            required = true
        });
    }
}