Symfony 3 senior dev assistance

Hi there, We need a proof of concept only - for a skilled senior Symfony 3 dev it should be 1-2 hours max to figure out whether it's possible or not. This is just an experiment so doesn't need a full development. Here's what we need: We have Symfony 3 project that contains login, call it app.web.com. We also have non-symfony web under web.com. What we need is a proof of concept that logging in via simple PHP (that can load Symfony 3 libraries if necessary) on [login to view URL] form we can log in both to [login to view URL] and [login to view URL] without the need of logging in twice. I seem to be lost on firewall part as far as I can see but maybe it's just not possible. As mentioned this is not a project, this is just assistance needed, you can either use our code or use your own (out of the box Symfony 3). We have FOSUserBundle for logging in Symfony. To acknowledge that you read and understood the project in your bid please write "firewall" otherwise your bid won't be accepted.